16 July 2026 · DMARC Engine · 40 min read
Introduction to DMARC and Subdomain Delegation
Domain-based Message Authentication, Reporting, and Conformance (DMARC) is a crucial email authentication protocol that helps organisations protect their domain from being used in phishing and spam attacks. By implementing DMARC, organisations can specify which email senders are authorised to send emails on their behalf, and which ones should be blocked. This is particularly important for franchises and multi-tenant systems, where a single domain may be used by multiple entities, making it harder to manage and secure email authentication.
To understand the importance of DMARC and subdomain delegation, let's consider a real-world example. Suppose we have a large franchise network, such as a hotel chain, with multiple locations using the same domain, for instance, hotelchain.com. Each location may have its own email system, and some may use third-party services to send emails. Without DMARC, it would be difficult for the hotel chain to ensure that only authorised emails are sent from their domain, making it vulnerable to phishing attacks.
DMARC works by checking the alignment of the From domain in an email with the domain of the email sender. There are two types of alignment: SPF (Sender Policy Framework) alignment and DKIM (DomainKeys Identified Mail) alignment. SPF alignment checks if the IP address of the email sender is authorised to send emails on behalf of the domain, while DKIM alignment checks if the email has been signed with a valid digital signature.
For example, if we have a DMARC record for the domain hotelchain.com, it may look like this:
_v2.hotelchain.com. IN TXT "v=DMARC1; p=none; pct=100; rua=mailto:abuse@hotelchain.com; ruf=mailto:forensics@hotelchain.com; fo=1"This record specifies that the domain hotelchain.com is using DMARC version 1, with a policy of none, meaning that emails that fail DMARC checks will not be blocked. The pct parameter specifies that 100% of emails should be checked, and the rua and ruf parameters specify the email addresses where aggregate and forensic reports should be sent.
However, for franchises and multi-tenant systems, implementing DMARC at the domain level may not be sufficient. This is because different entities within the organisation may have their own email systems, and some may use third-party services to send emails. In such cases, it may be necessary to implement DMARC at the subdomain level, using a process called subdomain delegation.
Subdomain delegation allows organisations to delegate DMARC management to subdomains, making it easier to manage email authentication for multiple entities within the organisation. For example, if we have a subdomain london.hotelchain.com for a hotel location in London, we can create a separate DMARC record for this subdomain, like this:
_v2.london.hotelchain.com. IN TXT "v=DMARC1; p=quarantine; pct=100; rua=mailto:abuse@london.hotelchain.com; ruf=mailto:forensics@london.hotelchain.com; fo=1"This record specifies a DMARC policy for the subdomain london.hotelchain.com, with a policy of quarantine, meaning that emails that fail DMARC checks will be quarantined. The rua and ruf parameters specify the email addresses where aggregate and forensic reports should be sent for this subdomain.
By using subdomain delegation, organisations can optimise their DMARC configuration to meet the specific needs of each entity within the organisation, while also improving the overall security and deliverability of their emails. In the next section, we will explore the challenges of implementing DMARC at the subdomain level for franchises and multi-tenant systems.
Understanding Franchises and Multi-Tenant Systems
Franchises and multi-tenant systems are complex organisational structures that comprise multiple entities operating under a single brand or umbrella. These entities can be separate businesses, subsidiaries, or departments, each with their own domain or subdomain. For instance, a large retail franchise like Marks & Spencer may have multiple subdomains for different regions, such as london.marksandspencer.co.uk or birmingham.marksandspencer.co.uk. Similarly, a multi-tenant system like a university may have separate subdomains for different departments, such as maths.university.ac.uk or engineering.university.ac.uk.
In these types of systems, email communication is critical for both internal and external purposes. Each entity may have its own email infrastructure, with multiple mail servers and domains. This can lead to a complex email ecosystem, with multiple senders, receivers, and mail streams. For example, a franchise may have a centralised email system for corporate communications, while individual franchisees may have their own email systems for local communications.
To illustrate this complexity, consider a real-world example. Suppose we have a franchise network with multiple subdomains, each with its own mail server. The DNS records for this network might look like this:
; Zone file for example.com
example.com. IN MX 10 mail.example.com
london.example.com. IN MX 10 mail.london.example.com
birmingham.example.com. IN MX 10 mail.birmingham.example.comIn this example, the franchise network has a central mail server mail.example.com and two regional mail servers mail.london.example.com and mail.birmingham.example.com. Each regional mail server is responsible for handling email for its respective subdomain.
Multi-tenant systems can be even more complex, with multiple tenants sharing the same domain or subdomain. For instance, a software-as-a-service (SaaS) provider may have multiple customers sharing the same domain, each with their own subdomain. The DNS records for this system might look like this:
; Zone file for saas-provider.com
saas-provider.com. IN MX 10 mail.saas-provider.com
customer1.saas-provider.com. IN MX 10 mail.customer1.saas-provider.com
customer2.saas-provider.com. IN MX 10 mail.customer2.saas-provider.comIn this example, the SaaS provider has a central mail server mail.saas-provider.com and two customer-specific mail servers mail.customer1.saas-provider.com and mail.customer2.saas-provider.com. Each customer has their own subdomain and mail server, which can lead to a complex email ecosystem.
The colour and branding of email communications can also vary across different entities in a franchise or multi-tenant system. For example, a franchise may have a centralised branding team that ensures consistency across all email communications, while individual franchisees may have their own branding and colour schemes. This can lead to a diverse range of email templates, each with its own unique design and content.
To optimise email deliverability in these complex systems, it is essential to have a clear understanding of the organisational structure and email ecosystem. This includes identifying all the entities involved, their respective domains and subdomains, and their email infrastructure. It also requires a deep understanding of the email streams and mail flows within the system, including the types of email being sent, the frequency of emails, and the recipients of those emails.
In the centre of this complexity is the need for a robust email authentication and security framework. This is where DMARC comes in, providing a way to authenticate email senders and prevent spam and phishing attacks. However, implementing DMARC in a franchise or multi-tenant system can be challenging, particularly when it comes to subdomain delegation. In the next section, we will explore the challenges of implementing DMARC at the subdomain level and how subdomain delegation can provide a solution for complex organisational structures.
Challenges of Implementing DMARC at the Subdomain Level
Implementing DMARC at the subdomain level can be a complex task, particularly for franchises and multi-tenant systems, where a central organisation manages a large number of subdomains, each with its own set of users, mail servers, and security requirements. One of the main challenges is the sheer scale of the operation, as each subdomain needs to be configured individually, with its own set of DMARC records, SPF, and DKIM settings. For example, a large franchise network with hundreds of subdomains, each representing a different location or brand, would require a significant amount of time and resources to set up and manage.
Another challenge is the lack of standardisation in subdomain naming conventions, which can make it difficult to implement a consistent DMARC policy across all subdomains. For instance, a franchise network may have subdomains named after locations, such as london.example.com and manchester.example.com, while others may be named after brands, such as brandx.example.com and brandy.example.com. This lack of standardisation can lead to errors and inconsistencies in DMARC record configuration, which can compromise the security of the entire domain.
In addition, franchises and multi-tenant systems often have complex organisational structures, with multiple departments, teams, and third-party vendors, each with their own email infrastructure and security requirements. This can make it difficult to coordinate DMARC implementation and management across all subdomains, particularly if each department or team has its own IT infrastructure and security policies. For example, a franchise network may have a central IT department that manages the overall email infrastructure, but each location or brand may have its own IT team that manages its own email servers and security settings.
To illustrate the complexity of implementing DMARC at the subdomain level, consider the following example of a DMARC record for a subdomain:
_dmarc.example.com. IN TXT "v=DMARC1; p=none; pct=100; rua=mailto:dmarc@example.com; ruf=mailto:dmarc@example.com; fo=1"This record specifies the DMARC policy for the example.com subdomain, including the version, policy, percentage of messages to apply the policy to, and the email addresses to send aggregate and failure reports to. However, in a franchise or multi-tenant system, this record would need to be replicated for each subdomain, with the correct settings and email addresses for each one.
On top of that, the process of generating and deploying DMARC records for each subdomain can be time-consuming and prone to errors, particularly if done manually. For example, a franchise network with hundreds of subdomains may need to generate and deploy hundreds of DMARC records, each with its own set of settings and email addresses. This can be a daunting task, especially if the organisation lacks the necessary expertise and resources to manage the process.
The colour coding and visualisation of DMARC records can also be a challenge, particularly for large and complex domains. For instance, a franchise network may use a colour-coded system to indicate the DMARC status of each subdomain, with green indicating a valid DMARC record, yellow indicating a warning, and red indicating an error. However, this can be difficult to manage and visualise, particularly if the organisation has hundreds of subdomains to monitor.
To optimise the DMARC implementation process, franchises and multi-tenant systems can use automation tools and scripts to generate and deploy DMARC records for each subdomain. For example, a franchise network can use a script to generate DMARC records for each subdomain, based on a set of predefined templates and settings. This can help to reduce errors and inconsistencies, and make it easier to manage the DMARC implementation process.
In terms of centre of excellence, franchises and multi-tenant systems can establish a central team or function to manage DMARC implementation and management across all subdomains. This team can provide guidance and support to each department or team, and help to ensure that DMARC records are configured correctly and consistently across all subdomains. For example, a franchise network can establish a central IT security team that manages the overall DMARC implementation and provides support to each location or brand.
Overall, implementing DMARC at the subdomain level can be a complex and challenging task, particularly for franchises and multi-tenant systems. However, by using automation tools and scripts, establishing a central team or function, and optimising the DMARC implementation process, organisations can help to ensure the security and integrity of their email infrastructure, and protect their customers and users from spam and phishing attacks. For instance, a franchise network can use a combination of automation tools and central management to implement DMARC across all subdomains, and provide a high level of security and protection for its customers and users.
The following is an example of a script that can be used to generate DMARC records for each subdomain:
import dns.resolver
def generate_dmarc_record(subdomain, domain, policy, pct, rua, ruf, fo):
record = "_dmarc.{}. IN TXT \"v=DMARC1; p={}; pct={}; rua=mailto:{}; ruf=mailto:{}; fo={}\"".format(subdomain, policy, pct, rua, ruf, fo)
return record
# Define the subdomains, domain, policy, percentage, and email addresses
subdomains = ["london", "manchester", "brandx", "brandy"]
domain = "example.com"
policy = "none"
pct = "100"
rua = "dmarc@example.com"
ruf = "dmarc@example.com"
fo = "1"
# Generate the DMARC records for each subdomain
for subdomain in subdomains:
record = generate_dmarc_record(subdomain, domain, policy, pct, rua, ruf, fo)
print(record)This script generates DMARC records for each subdomain, based on a set of predefined templates and settings. The script can be customised to fit the specific needs of the organisation, and can be used to generate DMARC records for hundreds of subdomains.
In addition to using scripts and automation tools, franchises and multi-tenant systems can also use third-party services to help manage the DMARC implementation process. For example, a franchise network can use a third-party service to generate and deploy DMARC records for each subdomain, and to provide monitoring and reporting on DMARC implementation and effectiveness. These services can help to reduce the complexity and cost of DMARC implementation, and can provide a high level of security and protection for customers and users.
To illustrate the benefits of using third-party services, consider the following example of a DMARC implementation report for a franchise network:
Subdomain DMARC Status SPF Status DKIM Status
london.example.com Valid Valid Valid
manchester.example.com Valid Valid Valid
brandx.example.com Error Valid Valid
brandy.example.com Warning Valid ValidThis report shows the DMARC status for each subdomain, including the SPF and DKIM status. The report can be used to identify errors and inconsistencies in DMARC implementation, and to provide guidance on how to improve DMARC effectiveness. By using third-party services to generate and deploy DMARC records, and to provide monitoring and reporting on DMARC implementation and effectiveness, franchises and multi-tenant systems can help to ensure the security and integrity of their email infrastructure, and protect their customers and users from spam and phishing attacks.
Subdomain Delegation: A Solution for Complex Organisational Structures
For organisations with complex structures, such as franchises or multi-tenant systems, implementing Domain-based Message Authentication, Reporting, and Conformance (DMARC) can be a daunting task. These organisations often have multiple subdomains, each with its own set of users, mail servers, and security requirements. Subdomain delegation offers a solution to this problem, allowing organisations to optimise their DMARC configuration and improve email deliverability.
Subdomain delegation involves creating a separate DMARC record for each subdomain, rather than relying on a single record at the organisational domain level. This approach provides greater flexibility and control, enabling organisations to tailor their DMARC configuration to the specific needs of each subdomain. For example, a franchise with multiple locations may want to implement a stricter DMARC policy for its corporate subdomain, while allowing for more relaxed settings on its store-level subdomains.
To illustrate this concept, let's consider a real-world example. Suppose we have a franchise called "CoffeeShop" with multiple locations, each with its own subdomain. The organisational domain is coffeeshop.com, and the subdomains are london.coffeeshop.com, paris.coffeeshop.com, and newyork.coffeeshop.com. Each subdomain has its own mail server and set of users. To implement subdomain delegation, we would create separate DMARC records for each subdomain, as shown in the following code snippets:
; DMARC record for london.coffeeshop.com
_london._dmarc.coffeeshop.com. IN TXT "v=DMARC1; p=reject; pct=100; rua=mailto:dmarc-london@coffeeshop.com; ruf=mailto:dmarc-london@coffeeshop.com; fo=1"
; DMARC record for paris.coffeeshop.com
_paris._dmarc.coffeeshop.com. IN TXT "v=DMARC1; p=none; pct=100; rua=mailto:dmarc-paris@coffeeshop.com; ruf=mailto:dmarc-paris@coffeeshop.com; fo=1"
; DMARC record for newyork.coffeeshop.com
_newyork._dmarc.coffeeshop.com. IN TXT "v=DMARC1; p=quarantine; pct=100; rua=mailto:dmarc-newyork@coffeeshop.com; ruf=mailto:dmarc-newyork@coffeeshop.com; fo=1"In this example, each subdomain has its own DMARC record with a unique policy setting. The london.coffeeshop.com subdomain has a reject policy, while the paris.coffeeshop.com subdomain has a none policy, and the newyork.coffeeshop.com subdomain has a quarantine policy. This allows the organisation to tailor its DMARC configuration to the specific needs of each location.
Subdomain delegation also provides benefits in terms of reporting and monitoring. With separate DMARC records for each subdomain, organisations can receive more detailed and accurate reports on email authentication and delivery issues. This enables them to identify and address problems more quickly, improving overall email deliverability and reducing the risk of spam and phishing attacks.
Another advantage of subdomain delegation is that it allows organisations to test and implement new DMARC policies on a smaller scale, before rolling them out to the entire organisation. For example, a franchise may want to test a new DMARC policy on a single subdomain, such as a store-level subdomain, before implementing it on the corporate subdomain. This approach helps to minimise the risk of disrupting email services and ensures a smoother transition to the new policy.
In addition to franchises, subdomain delegation can also be beneficial for multi-tenant systems, such as cloud-based email services or software-as-a-service (SaaS) providers. These systems often have multiple customers or tenants, each with their own subdomain and set of users. By implementing subdomain delegation, these systems can provide each tenant with a customised DMARC configuration, improving email deliverability and security for all users.
To implement subdomain delegation, organisations will need to work with their IT and email teams to configure the necessary DNS records and mail server settings. This may involve creating new DNS zones for each subdomain, as well as updating mail server configurations to support the new DMARC policies. Organisations may also need to invest in additional infrastructure, such as email gateways or security appliances, to support the increased complexity of their DMARC configuration.
In terms of best practices, organisations should ensure that they have a clear understanding of their subdomain structure and email architecture before implementing subdomain delegation. This includes identifying all subdomains, mail servers, and users, as well as mapping out the email flow and authentication processes. Organisations should also establish a centralised management system for their DMARC configuration, to ensure that all subdomains are properly configured and monitored.
Overall, subdomain delegation offers a powerful solution for organisations with complex structures, allowing them to optimise their DMARC configuration and improve email deliverability. By providing greater flexibility and control, subdomain delegation enables organisations to tailor their DMARC policy to the specific needs of each subdomain, improving email security and reducing the risk of spam and phishing attacks. As organisations continue to evolve and grow, subdomain delegation will play an increasingly important role in helping them to manage their email infrastructure and maintain a strong online presence.
Technical Considerations for DMARC Subdomain Delegation
When implementing DMARC subdomain delegation, several technical considerations must be taken into account to ensure a smooth and effective setup. One of the primary concerns is the organisational structure of the franchise or multi-tenant system, as this will dictate the complexity of the DMARC configuration. For instance, a large franchise network with multiple subdomains, each representing a different location or brand, will require a more intricate DMARC setup compared to a smaller organisation with fewer subdomains.
To begin with, it is essential to understand the DNS structure of the organisation, including the parent domain and all subdomains. This information will be used to configure the DMARC records, which are typically published as TXT records in the DNS. The DMARC record for the parent domain will serve as the foundation for the subdomain delegation, and it is crucial to ensure that this record is correctly configured before proceeding with the subdomain setup.
A typical DMARC record for a parent domain might look like this:
_dmarc.example.com. IN TXT "v=DMARC1; p=none; pct=100; rua=mailto:dmarc@example.com; ruf=mailto:dmarc@example.com; fo=1"In this example, the DMARC record is published for the _dmarc.example.com subdomain, and it specifies the DMARC version, policy, and reporting options. The p tag sets the policy to none, which means that emails that fail DMARC validation will not be blocked or rejected. The pct tag sets the percentage of emails to which the policy applies, and the rua and ruf tags specify the email addresses to which aggregate and failure reports will be sent, respectively.
When delegating DMARC to subdomains, it is necessary to create a separate DMARC record for each subdomain. This record will inherit the settings from the parent domain's DMARC record, but it can also override these settings if required. For example, a subdomain might require a more restrictive policy or different reporting options. The subdomain DMARC record can be published as a TXT record in the subdomain's DNS, like this:
_dmarc.subdomain.example.com. IN TXT "v=DMARC1; p=quarantine; pct=100; rua=mailto:dmarc@subdomain.example.com; ruf=mailto:dmarc@subdomain.example.com; fo=1"In this example, the subdomain DMARC record overrides the policy set in the parent domain's record, setting it to quarantine instead of none. This means that emails that fail DMARC validation for this subdomain will be quarantined instead of being delivered to the recipient's inbox.
Another important consideration when implementing DMARC subdomain delegation is the use of organisational domains. An organisational domain is a domain that is used to identify the organisation or company, rather than a specific subdomain or brand. For example, a large franchise network might use an organisational domain such as franchisenetwork.com, with each location or brand having its own subdomain, such as location1.franchisenetwork.com or brand1.franchisenetwork.com.
When using organisational domains, it is essential to ensure that the DMARC record for the organisational domain is correctly configured, as this will affect all subdomains that use this domain. The organisational domain DMARC record can be used to set a default policy and reporting options for all subdomains, which can then be overridden by each subdomain's DMARC record if required.
In addition to the technical considerations mentioned above, it is also important to consider the reporting and monitoring aspects of DMARC subdomain delegation. DMARC reports provide valuable insights into the email authentication and delivery process, and they can be used to identify and troubleshoot issues with the DMARC configuration. When implementing DMARC subdomain delegation, it is essential to ensure that reporting is enabled for each subdomain, and that the reports are being sent to the correct email addresses.
To enable reporting for a subdomain, the rua and ruf tags can be used in the subdomain's DMARC record, like this:
_dmarc.subdomain.example.com. IN TXT "v=DMARC1; p=quarantine; pct=100; rua=mailto:dmarc@subdomain.example.com; ruf=mailto:dmarc@subdomain.example.com; fo=1"In this example, the rua tag specifies the email address to which aggregate reports will be sent, and the ruf tag specifies the email address to which failure reports will be sent. The fo tag is used to specify the format of the failure reports, with a value of 1 indicating that the reports should be sent in a compressed format.
Overall, implementing DMARC subdomain delegation requires careful planning and consideration of the technical aspects involved. By understanding the organisational structure, DNS setup, and reporting requirements, organisations can ensure a smooth and effective DMARC setup that provides the best possible protection against email-based threats. Whether you are a large franchise network or a multi-tenant system, DMARC subdomain delegation can help you to improve the security and authenticity of your email communications, and to better protect your brand and reputation.
The centre of any DMARC subdomain delegation strategy should be a comprehensive understanding of the organisation's email ecosystem, including all subdomains, email services, and authentication protocols. This will enable the organisation to optimise its DMARC configuration, ensure colour consistency across all subdomains, and organise its reporting and monitoring processes to provide the best possible insights into email authentication and delivery.
To optimise the DMARC configuration, organisations should consider using a DMARC reporting and analysis tool, which can provide detailed insights into email authentication and delivery, and help to identify areas for improvement. These tools can also help organisations to automate the process of monitoring and reporting, which can be time-consuming and labour-intensive, especially for large and complex email ecosystems.
In terms of reporting and monitoring, organisations should ensure that they have a clear understanding of the different types of DMARC reports, including aggregate and failure reports. Aggregate reports provide a summary of email authentication and delivery activity, while failure reports provide detailed information about individual emails that failed DMARC validation. By analysing these reports, organisations can identify and troubleshoot issues with their DMARC configuration, and make data-driven decisions to improve the security and authenticity of their email communications.
By taking a proactive and data-driven approach to DMARC subdomain delegation, organisations can ensure the best possible protection against email-based threats, and improve the overall security and authenticity of their email communications. This can help to protect the organisation's brand and reputation, and prevent financial losses due to email-based attacks.
In the context of a large franchise network, DMARC subdomain delegation can be used to improve the security and authenticity of email communications across all locations and brands. By implementing a consistent DMARC configuration across all subdomains, the franchise network can ensure that all emails are authenticated and verified, and that only legitimate emails are delivered to recipients. This can help to prevent email-based attacks, such as phishing and spoofing, and protect the franchise network's brand and reputation.
To implement DMARC subdomain delegation in a large franchise network, the organisation should start by identifying all subdomains and email services used across the network. This will enable the organisation to create a comprehensive DMARC configuration that covers all subdomains and email services, and ensures consistent authentication and verification of emails. The organisation should also consider using a DMARC reporting and analysis tool to provide detailed insights into email authentication and delivery, and to help identify areas for improvement.
By following these steps and taking a proactive and data-driven approach to DMARC subdomain delegation, large franchise networks and multi-tenant systems can improve the security and authenticity of their email communications, and protect their brand and reputation from email-based threats. This can help to prevent financial losses due to email-based attacks, and ensure the long-term success and stability of the organisation.
The benefits of DMARC subdomain delegation are clear, and organisations that implement this strategy can expect to see significant improvements in the security and authenticity of their email communications. By providing a consistent and comprehensive approach to email authentication and verification, DMARC subdomain delegation can help organisations to prevent email-based attacks, protect their brand and reputation, and ensure the long-term success and stability of the organisation.
In addition to the benefits mentioned above, DMARC subdomain delegation can also help organisations to improve their email deliverability and prevent emails from being blocked or rejected by recipient mail servers. By ensuring that all emails are authenticated and
Case Study: Implementing DMARC for a Large Franchise Network
A large franchise network, comprising over 500 individual franchisees, each with their own subdomain, presented a complex challenge for implementing Domain-based Message Authentication, Reporting, and Conformance (DMARC). The organisation, a well-known high street retailer, had a centralised IT function, but each franchisee was responsible for their own email marketing and customer communication. This decentralised approach made it difficult to maintain a consistent brand image and ensure the security of customer interactions.
The franchise network's email infrastructure was characterised by a mix of on-premise and cloud-based solutions, with some franchisees using third-party email service providers. This heterogeneity added to the complexity of implementing DMARC, as each subdomain required its own DMARC record. The central IT function recognised the need to optimise email deliverability and protect the brand's reputation, but the scale and diversity of the network made it a daunting task.
To begin the implementation process, the central IT function conducted an audit of all subdomains, identifying those that were actively sending email. This involved analysing email logs, DNS records, and consulting with franchisees to determine which subdomains were in use. The audit revealed that over 200 subdomains were sending email, with some using multiple email service providers. For example, the subdomain london.north.franchiseretailer.co.uk was using a combination of Mailchimp and Amazon SES to send marketing emails and transactional notifications.
The next step was to create a DMARC record for each subdomain. The central IT function decided to use a relaxed policy, starting with a p=none policy, to gather data on email authentication and identify potential issues. The DMARC record for the london.north.franchiseretailer.co.uk subdomain, for instance, looked like this:
_dmarc.london.north.franchiseretailer.co.uk. IN TXT "v=DMARC1; p=none; pct=100; rua=mailto:dmarc-aggregate@franchiseretailer.co.uk; ruf=mailto:dmarc-failure@franchiseretailer.co.uk; fo=1"This record specified that the subdomain was using DMARC version 1, with a none policy, and requested aggregate and failure reports be sent to designated email addresses.
As the DMARC records were deployed, the central IT function began to receive reports on email authentication. These reports highlighted issues with email alignment, where the sending domain did not match the domain in the From header. For example, some franchisees were using email service providers that were not configured to use the franchisee's subdomain in the From header, resulting in unauthenticated email. The central IT function worked with the franchisees to correct these issues, ensuring that all email was properly authenticated.
The DMARC reports also revealed issues with spam and phishing attacks, where malicious actors were spoofing the franchise network's domains. The central IT function used this data to identify and block suspicious email activity, improving the overall security of the franchise network's email infrastructure. To illustrate this, the following snippet from a DMARC aggregate report shows a suspicious email campaign that was blocked due to authentication failure:
{
"org_name": "Franchise Retailer",
"email": "dmarc-aggregate@franchiseretailer.co.uk",
"date_range": {
"start": "2022-01-01",
"end": "2022-01-07"
},
"records": [
{
"source_ip": "192.0.2.1",
"count": 100,
"disposition": "none",
"dkim": "fail",
"spf": "fail"
}
]
}This report indicated that 100 emails were sent from the IP address 192.0.2.1, with both DKIM and SPF authentication failing. The central IT function was able to use this data to block future email activity from this IP address, preventing potential spam and phishing attacks.
After several months of monitoring and refining the DMARC configuration, the central IT function decided to move to a more restrictive policy, setting p=quarantine for all subdomains. This policy change helped to further improve email deliverability and reduce the risk of spam and phishing attacks. The franchise network's email infrastructure was now more secure, with a consistent brand image and improved customer trust.
The implementation of DMARC for the large franchise network demonstrated the importance of careful planning, monitoring, and refinement. By starting with a relaxed policy and gradually moving to a more restrictive one, the central IT function was able to optimise email deliverability and protect the brand's reputation. The use of DMARC reports and data analysis was crucial in identifying and addressing issues with email authentication and security. As the franchise network continues to grow and evolve, the central IT function will need to remain vigilant, ensuring that the DMARC configuration remains effective and aligned with the organisation's overall security strategy.
To centre the DMARC configuration and make it more manageable, the central IT function decided to use a cloud-based DMARC management platform. This platform provided a single centre of control for all DMARC-related activities, allowing the IT team to easily monitor and update DMARC records, as well as analyse reports and identify potential issues. The colour coding and visualisation features of the platform also helped to simplify the process of identifying and addressing issues with email authentication and security.
In terms of subdomain delegation, the franchise network's DMARC implementation highlighted the importance of careful planning and organisation. The central IT function needed to ensure that each subdomain had its own DMARC record, and that these records were properly configured and aligned with the organisation's overall security strategy. The use of subdomain delegation also helped to improve the colour and consistency of the franchise network's brand image, as all email activity was now properly authenticated and aligned with the organisation's domain.
Overall, the implementation of DMARC for the large franchise network was a complex but ultimately successful project. The central IT function was able to optimise email deliverability, improve security, and protect the brand's reputation, while also ensuring that the organisation's email infrastructure remained scalable and flexible. By using a combination of careful planning, monitoring, and refinement, as well as the right tools and technologies, the franchise network was able to achieve a high level of email authentication and security, and to maintain a consistent brand image across all subdomains.
Best Practices for Managing DMARC Across Multiple Subdomains
Managing DMARC across multiple subdomains can be a complex task, particularly for franchises and multi-tenant systems. To optimise your DMARC configuration and ensure the security of your email ecosystem, it is essential to follow best practices. One key consideration is to maintain a centralised centre of control, where a single team or individual is responsible for managing DMARC across all subdomains. This helps to prevent inconsistencies and errors, which can lead to email delivery issues.
For example, a large franchise network with multiple subdomains, such as subdomain1.franchisename.co.uk and subdomain2.franchisename.co.uk, can benefit from a centralised approach. By setting up a DMARC record at the organisational domain level, such as franchisename.co.uk, the franchise can establish a baseline policy that applies to all subdomains. This can be achieved by publishing a DMARC record, such as:
_dmarc.franchisename.co.uk. IN TXT "v=DMARC1; p=none; pct=100; rua=mailto:dmarc@franchisename.co.uk; ruf=mailto:dmarc@franchisename.co.uk; fo=1" This record specifies the DMARC version, policy, and reporting options, and applies to all subdomains.
Another best practice is to use subdomain delegation, which allows the franchise to delegate control of DMARC to individual subdomains. This can be useful for franchises with multiple subdomains that require different DMARC policies. For instance, a subdomain used for marketing campaigns may require a more relaxed policy, while a subdomain used for transactional emails may require a stricter policy. Subdomain delegation can be achieved by publishing a DMARC record at the subdomain level, such as:
_dmarc.subdomain1.franchisename.co.uk. IN TXT "v=DMARC1; p=quarantine; pct=100; rua=mailto:dmarc@subdomain1.franchisename.co.uk; ruf=mailto:dmarc@subdomain1.franchisename.co.uk; fo=1" This record specifies the DMARC policy and reporting options for the subdomain1.franchisename.co.uk subdomain.
It is also essential to monitor and analyse DMARC reports to identify potential issues and optimise the DMARC configuration. DMARC reports provide valuable insights into email authentication and delivery, and can help the franchise to identify spoofing attempts and improve email deliverability. For example, a DMARC report may indicate that a particular subdomain is experiencing authentication issues, which can be addressed by adjusting the DMARC policy or updating the SPF record.
In addition to monitoring DMARC reports, it is crucial to maintain accurate and up-to-date DNS records, including SPF, DKIM, and DMARC records. Outdated or incorrect DNS records can lead to email delivery issues and compromise the security of the email ecosystem. For instance, an incorrect SPF record can cause emails to be flagged as spam, while an outdated DKIM record can prevent emails from being authenticated.
To ensure the colour of the email ecosystem remains secure, it is recommended to implement a DMARC policy that is aligned with the organisation's email security strategy. This may involve setting up a DMARC policy that rejects emails that fail authentication, or quarantining emails that fail authentication. For example, a franchise may choose to implement a DMARC policy that rejects emails that fail authentication, such as:
_dmarc.franchisename.co.uk. IN TXT "v=DMARC1; p=reject; pct=100; rua=mailto:dmarc@franchisename.co.uk; ruf=mailto:dmarc@franchisename.co.uk; fo=1" This record specifies a DMARC policy that rejects emails that fail authentication, which can help to prevent spoofing attempts and improve email deliverability.
Finally, it is vital to educate users about the importance of DMARC and email authentication, and to provide them with the necessary tools and resources to manage DMARC effectively. This may involve providing training and support, as well as implementing a system for monitoring and reporting DMARC issues. By following these best practices, franchises and multi-tenant systems can optimise their DMARC configuration, improve email deliverability, and enhance the security of their email ecosystem.
In the context of a large franchise network, managing DMARC across multiple subdomains can be a daunting task. However, by maintaining a centralised centre of control, using subdomain delegation, monitoring and analysing DMARC reports, maintaining accurate and up-to-date DNS records, implementing a DMARC policy that is aligned with the organisation's email security strategy, and educating users about the importance of DMARC and email authentication, franchises can ensure the security and integrity of their email ecosystem. By doing so, they can protect their brand reputation, prevent email-based attacks, and improve email deliverability, which is essential for maintaining strong customer relationships and driving business growth.
Overcoming Common Obstacles in DMARC Subdomain Delegation
Implementing DMARC subdomain delegation can be a complex task, particularly for large franchises and multi-tenant systems. Several obstacles may arise during this process, and it is essential to address these challenges to ensure a successful deployment. One common issue is the management of multiple subdomains, each requiring its own DMARC record. For instance, a large franchise with numerous locations may have a separate subdomain for each location, such as london.example.com, paris.example.com, and tokyo.example.com.
To manage these subdomains effectively, it is crucial to have a centralised system in place, allowing for easy organisation and monitoring of DMARC records. This can be achieved by using a dedicated domain management platform or by implementing a robust DNS management system.
A key aspect of managing multiple subdomains is the ability to optimise DMARC record configuration. This involves setting the correct policy, such as none, quarantine, or reject, and configuring the alignment, either relaxed or strict. The following example shows a basic DMARC record for a subdomain:
_dmarc.example.com. IN TXT "v=DMARC1; p=none; pct=100; rua=mailto:dmarc@example.com"This record specifies the DMARC version, policy, percentage of emails to apply the policy to, and the email address to send aggregate reports to.
Another common obstacle is the need to delegate subdomains to third-party service providers, such as email service providers or marketing automation platforms. This requires careful planning to ensure that the subdomain delegation is set up correctly, allowing the third-party provider to send emails on behalf of the franchise or multi-tenant system.
For example, a franchise may use a third-party email service provider to send marketing emails from a subdomain such as marketing.example.com. To enable this, the franchise needs to configure the subdomain delegation, allowing the email service provider to authenticate emails sent from this subdomain.
The following is an example of a DMARC record that includes a third-party service provider:
_dmarc.marketing.example.com. IN TXT "v=DMARC1; p=quarantine; pct=100; rua=mailto:dmarc@example.com; aspf=s; adkb=dkim:s; v=dkim; k=rsa; p=dkim_public_key"This record includes the DMARC policy, alignment, and public key for DKIM authentication, as well as the email address to send aggregate reports to.
In some cases, the third-party service provider may require a custom DMARC record configuration, which can add complexity to the implementation process. It is essential to work closely with the service provider to ensure that the DMARC record is configured correctly and that emails sent from the subdomain are properly authenticated.
To overcome these obstacles, it is recommended to develop a comprehensive plan for implementing DMARC subdomain delegation. This plan should include the following steps:
1. Identify all subdomains that require DMARC implementation
2. Determine the DMARC policy and alignment for each subdomain
3. Configure the DMARC records for each subdomain
4. Test the DMARC implementation to ensure correct functionality
5. Monitor the DMARC reports to identify any issues or errors
By following these steps and working closely with third-party service providers, franchises and multi-tenant systems can successfully implement DMARC subdomain delegation, improving the security and deliverability of their emails.
The use of tools such as DMARC analyzers and DNS management platforms can also help to simplify the process of implementing and managing DMARC subdomain delegation. These tools provide a centralised interface for managing DMARC records, monitoring DMARC reports, and analysing email sending patterns.
For example, a DMARC analyser can help to identify issues with DMARC record configuration, such as incorrect policy settings or missing alignment. The following is an example of a DMARC report that highlights issues with DMARC record configuration:
Subject: DMARC report for example.com
Date: 2023-02-20
Domain: example.com
Organizational domain: example.com
Source IP: 192.0.2.1
Source IP owner: example.com
Auth failures: 10
Reason: Alignment issueThis report indicates that there are issues with the alignment of the DMARC record, which may be causing authentication failures.
By using these tools and developing a comprehensive plan, franchises and multi-tenant systems can overcome the common obstacles associated with implementing DMARC subdomain delegation, ensuring the security and deliverability of their emails.
In addition to the technical aspects of implementing DMARC subdomain delegation, it is also essential to consider the organisational aspects. This includes ensuring that all stakeholders are aware of the DMARC implementation and its benefits, as well as providing training on how to manage and monitor DMARC records.
For example, a large franchise may need to provide training to its IT staff on how to configure and manage DMARC records for each subdomain. This training should cover topics such as DMARC policy settings, alignment, and aggregate report analysis.
By considering both the technical and organisational aspects of implementing DMARC subdomain delegation, franchises and multi-tenant systems can ensure a successful deployment and improve the overall security and deliverability of their emails.
The colour of the DMARC implementation can also be affected by the organisational structure of the franchise or multi-tenant system. For instance, a franchise with a complex organisational structure may require a more sophisticated DMARC implementation, with multiple subdomains and third-party service providers.
In such cases, it is essential to have a clear understanding of the organisational structure and how it will impact the DMARC implementation. This includes identifying the different departments, locations, and third-party service providers that will be involved in the implementation.
By having a clear understanding of the organisational structure, franchises and multi-tenant systems can develop a tailored approach to implementing DMARC subdomain delegation, ensuring that the solution meets their specific needs and requirements.
To centre the DMARC implementation around the organisational structure, it is recommended to conduct a thorough analysis of the organisation's email sending patterns and requirements. This analysis should include identifying the different types of emails sent by the organisation, such as marketing emails, transactional emails, and internal emails.
The analysis should also identify the different departments and locations that send emails, as well as any third-party service providers used by the organisation.
By conducting this analysis, franchises and multi-tenant systems can gain a deeper understanding of their email sending patterns and requirements, enabling them to develop a more effective DMARC implementation that meets their specific needs.
The analysis can also help to identify any potential issues or risks associated with the DMARC implementation, such as alignment issues or authentication failures.
By identifying these issues early on, franchises and multi-tenant systems can take steps to mitigate them, ensuring a successful DMARC implementation that improves the security and deliverability of their emails.
In the context of a large franchise or multi-tenant system, the DMARC implementation should be designed to be flexible and adaptable, allowing for easy optimise and update of DMARC records as required.
This can be achieved by using a modular approach to implementing DMARC, with each subdomain having its own DMARC record that can be easily updated or modified as needed.
The use of automation tools can also help to simplify the process of managing and updating DMARC records, enabling franchises and multi-tenant systems to quickly respond to changes in their email sending patterns or requirements.
By taking a flexible and adaptable approach to implementing DMARC, franchises and multi-tenant systems can ensure that their DMARC implementation remains effective and efficient over time, even as their email sending patterns and requirements change.
Overall, overcoming the common obstacles associated
Future-Proofing Your DMARC Configuration for Scalability and Security
To ensure the long-term effectiveness of your Domain-based Message Authentication, Reporting, and Conformance (DMARC) configuration, particularly in complex organisational structures such as franchises and multi-tenant systems, it is crucial to adopt a forward-thinking approach. This involves optimising your setup to accommodate growth, enhancing security measures, and maintaining flexibility to adapt to evolving email authentication standards and potential threats.
A key aspect of future-proofing your DMARC configuration is to organise your domain structure in a way that facilitates easy management and scalability. For instance, utilising subdomain delegation allows each franchise or tenant to manage their own DMARC settings without compromising the overall domain's security posture. This can be achieved by creating a separate DMARC record for each subdomain, as illustrated in the following example:
; DMARC record for a subdomain (e.g., franchise1.example.com)
_dmarc.franchise1.example.com. IN TXT "v=DMARC1; p=none; pct=100; rua=mailto:dmarc_agg@example.com; ruf=mailto:dmarc_forensics@example.com; fo=1"In this example, franchise1.example.com has its own DMARC policy (p=none), indicating that emails failing DMARC checks should not be blocked or quarantined, but rather reported back to the aggregator and forensic email addresses specified. This setup enables each subdomain to operate under its own DMARC policy, which is particularly useful for franchises or multi-tenant systems where different entities may have varying requirements or levels of email authentication maturity.
Another critical component of future-proofing is to ensure that your DMARC configuration is aligned with other email authentication protocols, such as Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM). SPF helps prevent spam by verifying that emails are sent from IP addresses authorised by the domain owner, while DKIM cryptographically signs emails to verify their authenticity. For optimal security and deliverability, it is essential that these protocols are properly configured and aligned with your DMARC setup.
For example, an SPF record might look like this:
; SPF record for example.com
example.com. IN TXT "v=spf1 ip4:192.0.2.1 ip4:198.51.100.1 include:_spf.example.net -all"This record specifies the IP addresses from which emails can be sent on behalf of example.com, including the IP addresses 192.0.2.1 and 198.51.100.1, and the SPF record of _spf.example.net. The -all directive at the end indicates that emails from IP addresses not listed should be rejected.
Similarly, a DKIM record might be configured as follows:
; DKIM record for example.com
default._domainkey.example.com. IN TXT "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCq1RbLiJ18oyyB/6giTjVOH2TnR7jP9nH6W0O5HjUh+H3uXMXHk2m3x4hKfNh4K0wSAkQH0RjQ5RzG7j7j6Wf4gyqT6KuJzH7aX7J4L6k/5TjP9nH6W0O5HjUh+H3uXMXHk2m3x4hKfNh4K0wSAkQH0RjQ5RzG7j7j6Wf4gyqT6KuJ"This DKIM record specifies the public key used for verifying the DKIM signature of emails sent from example.com.
To maintain the security and integrity of your email ecosystem, it is also vital to regularly monitor DMARC reports and adjust your configuration as needed. These reports provide valuable insights into email authentication issues, such as alignment problems or SPF and DKIM failures, which can be used to refine your DMARC policy and improve overall email deliverability.
For instance, if DMARC reports indicate a high volume of emails failing SPF checks due to unauthorised senders, you may need to update your SPF record to include additional IP addresses or adjust your DMARC policy to a more restrictive setting (e.g., p=quarantine or p=reject). Conversely, if reports show a significant number of emails passing DMARC checks but still being flagged as spam, it may be necessary to investigate other factors influencing deliverability, such as email content, sender reputation, or the presence of spam triggers.
In addition to technical considerations, future-proofing your DMARC configuration involves staying informed about the latest developments in email authentication and security. This includes keeping abreast of updates to DMARC and other email authentication protocols, as well as emerging threats and best practices in the field. Participating in industry forums, attending relevant conferences, and engaging with email security communities can provide valuable opportunities for knowledge sharing and collaboration.
Lastly, implementing a robust incident response plan is crucial for addressing potential security breaches or email authentication issues that may arise. This plan should outline procedures for responding to DMARC-related incidents, such as a sudden spike in authentication failures or the detection of phishing attacks exploiting vulnerabilities in your email ecosystem. By having a well-defined incident response plan in place, you can minimise the impact of security incidents and ensure a rapid recovery, thereby protecting your organisation's reputation and maintaining the trust of your customers and stakeholders.
In short, future-proofing your DMARC configuration for scalability and security requires a multifaceted approach that encompasses technical optimisation, alignment with other email authentication protocols, regular monitoring and analysis of DMARC reports, staying informed about the latest developments in email security, and implementing a robust incident response plan. By adopting this proactive and comprehensive strategy, you can ensure the long-term effectiveness of your DMARC setup, protect your organisation from emerging email-based threats, and maintain a strong security posture in an ever-evolving digital landscape.