23 July 2026 · DMARC Engine · 39 min read
The Third-Party Sender Conundrum
Domains with high volume third-party senders often face a unique set of challenges when it comes to optimising DMARC. The primary issue arises from the need to balance security with deliverability, as overly restrictive DMARC policies can lead to false positives, resulting in legitimate emails being blocked. On the other hand, a policy that is too permissive can leave the domain vulnerable to phishing attacks.
For instance, consider a company like example.co.uk, which uses a marketing automation platform like Marketo to send newsletters to its subscribers. The Marketo platform may use its own IP addresses to send emails, which can cause issues with DMARC alignment if not properly configured.
_v=DMARC1; p=none; pct=100; rua=mailto:aggrep@example.co.uk; ruf=mailto:forensics@example.co.uk; fo=1In this example, the DMARC record for example.co.uk is set to monitor mode (p=none), which allows the company to gather data on email senders without affecting deliverability. However, this approach may not be suitable for all domains, particularly those with a high volume of third-party senders.
One common mistake is to assume that adding all third-party senders to the SPF record will resolve the issue. While this may seem like a straightforward solution, it can lead to SPF record length issues, particularly if the domain has a large number of third-party senders.
v=spf1 include:_spf.marketo.com include:_spf.salesforce.com include:_spf.amazonaws.com -allIn this example, the SPF record for example.co.uk includes several third-party senders, but this approach can become cumbersome to manage, especially if the domain has a large number of senders.
A better approach is to use a combination of SPF and DKIM to authenticate emails. By using DKIM, the domain can ensure that emails are authenticated at the message level, rather than just at the IP address level. This can help to prevent spoofing attacks and improve deliverability.
For hosted or managed setups, such as those offered by DMARC Engine, the process of managing third-party senders is often simplified through the use of automated tools and workflows. These tools can help to streamline the process of adding and removing third-party senders, as well as monitoring DMARC reports to identify potential issues.
In terms of specific recommendations, it is essential to regularly review and update the DMARC record to ensure that it reflects the current set of third-party senders. This can be done by monitoring aggregate reports and adjusting the DMARC policy as needed. Also, using a DMARC analytics tool can help to provide insights into email senders and identify potential issues before they become major problems.
Ultimately, the key to optimising DMARC for domains with high volume third-party senders is to strike a balance between security and deliverability. By using a combination of SPF and DKIM, and regularly monitoring and updating the DMARC record, domains can help to prevent phishing attacks while ensuring that legitimate emails are delivered to subscribers.
It is also crucial to consider the impact of DMARC on the domain's overall email ecosystem. For example, if the domain has a high volume of emails being sent via third-party senders, it may be necessary to adjust the DMARC policy to reflect this. This can involve setting a more permissive policy, such as p=quarantine, to ensure that legitimate emails are not blocked.
_v=DMARC1; p=quarantine; pct=100; rua=mailto:aggrep@example.co.uk; ruf=mailto:forensics@example.co.uk; fo=1In this example, the DMARC record for example.co.uk is set to quarantine mode (p=quarantine), which allows the company to flag emails that fail DMARC authentication without blocking them. This approach can help to prevent false positives while still providing an additional layer of security.
By taking a thoughtful and multi-faceted approach to DMARC optimisation, domains with high volume third-party senders can help to ensure the security and deliverability of their emails, while also protecting their brand and subscribers from phishing attacks.
Assessing Current DMARC Configuration
When dealing with domains that have high volume third-party senders, it is crucial to assess the current DMARC configuration to understand the centre of the issue. This involves examining the existing DMARC record, SPF, and DKIM configurations to identify potential misalignments or gaps that could be impacting deliverability. A common mistake is to assume that a DMARC record is correctly configured simply because it exists.
For instance, a domain may have a DMARC record with a policy set to none, which can lead to a false sense of security, as it does not actually enforce any policy.
_dmarc.example.com. IN TXT "v=DMARC1; p=none; pct=100; rua=mailto:aggrep@example.com; ruf=mailto:forensics@example.com; fo=1" In this example, the p=none policy means that the domain is not enforcing any DMARC policy, and the pct=100 tag means that the policy is applied to 100% of messages. However, without a hosted or managed setup to handle the aggregate reports, the rua and ruf tags may not be effective in providing useful feedback.
At DMARC Engine, we have seen cases where the DMARC record is not properly aligned with the SPF and DKIM configurations, leading to authentication failures and deliverability issues. For example, a domain may have an SPF record that includes a third-party sender's IP address, but the DMARC record does not account for this sender.
example.com. IN TXT "v=spf1 include:thirdpartysender.com -all" In this case, the SPF record includes the third-party sender's domain, but the DMARC record does not have an aspf tag to specify the alignment mode for SPF. This can lead to authentication failures and deliverability issues.
To optimise the DMARC configuration, it is essential to assess the current setup and identify any gaps or misalignments. This involves reviewing the DMARC record, SPF, and DKIM configurations, as well as analysing the aggregate report data to understand the authentication results.
In a hosted or managed setup, such as DMARC Engine, the process of assessing the current DMARC configuration is simplified, as the platform provides tools and expertise to analyse the configuration and identify potential issues. However, in a self-managed setup, it is crucial to have a thorough understanding of the DMARC configuration and its interactions with SPF and DKIM.
A key consideration when assessing the current DMARC configuration is the colour of the traffic, in terms of legitimate and malicious email. A domain with high volume third-party senders may have a higher risk of phishing attacks, which can impact the deliverability of legitimate email.
To mitigate this risk, it is essential to implement a DMARC policy that balances security and deliverability. This may involve setting a policy of quarantine or reject for unauthenticated email, while also ensuring that legitimate email is properly authenticated and aligned with the domain's DMARC configuration.
Ultimately, assessing the current DMARC configuration is a critical step in optimising DMARC for domains with high volume third-party senders. By understanding the centre of the issue and identifying potential gaps or misalignments, it is possible to implement a DMARC configuration that balances security and deliverability, and ensures the best possible outcome for the domain.
In our experience at DMARC Engine, a thorough assessment of the current DMARC configuration is essential to optimise the setup for high volume third-party senders. This involves a detailed analysis of the DMARC record, SPF, and DKIM configurations, as well as the aggregate report data, to identify potential issues and implement a configuration that meets the domain's specific needs.
By taking a proactive approach to assessing and optimising the DMARC configuration, domains with high volume third-party senders can improve their deliverability and reduce the risk of phishing attacks, while also ensuring that legitimate email is properly authenticated and aligned with the domain's DMARC configuration.
To achieve this, it is crucial to have a deep understanding of the DMARC configuration and its interactions with SPF and DKIM, as well as the ability to analyse aggregate report data and implement a DMARC policy that balances security and deliverability.
In the next section, we will discuss how to understand aggregate report data, which is a critical component of assessing and optimising the DMARC configuration.
Understanding Aggregate Report Data
To optimise DMARC for domains with high volume third-party senders, it is crucial to understand the aggregate report data, which provides insights into the email sending patterns and authentication results of your domain. The aggregate reports, also known as Reporting Using Aggregate Data, or RUA, are typically sent to the email address specified in the DMARC record, and they contain a wealth of information about the emails sent from your domain.
When analysing aggregate reports, it is essential to consider the reporting format, which is usually in XML, and the data elements included, such as the source IP address, email authentication results, and message disposition. For instance, a typical aggregate report might contain the following data:
<feedback>
<report_metadata>
<org_name>example.com</org_name>
<email>abuse@example.com</email>
<extra_contact_info>https://example.com/dmarc</extra_contact_info>
<report_id>1234567890</report_id>
<date_range>
<begin>2022-01-01T00:00:00Z</begin>
<end>2022-01-07T23:59:59Z</end>
</date_range>
</report_metadata>
<policy_published>
<domain>example.com</domain>
<adkim>r</adkim>
<aspf>r</aspf>
<p>none</p>
<sp>none</sp>
<pct>100</pct>
</policy_published>
<record>
<row>
<source_ip>192.0.2.1</source_ip>
<count>10</count>
<policy_evaluated>
<disposition>none</disposition>
<dkim>pass</dkim>
<spf>pass</spf>
</policy_evaluated>
</row>
<row>
<source_ip>198.51.100.1</source_ip>
<count>5</count>
<policy_evaluated>
<disposition>quarantine</disposition>
<dkim>fail</dkim>
<spf>fail</spf>
</policy_evaluated>
</row>
</record>
</feedback>In this example, the report indicates that there were 10 emails sent from the IP address 192.0.2.1, which passed both DKIM and SPF authentication, and 5 emails sent from the IP address 198.51.100.1, which failed both DKIM and SPF authentication.
When reviewing aggregate reports, it is vital to pay attention to the authentication results, as they can indicate potential issues with your DMARC configuration or email sending infrastructure. For instance, if you notice a high volume of emails failing SPF authentication, it may indicate that your SPF record is not correctly configured or that there are unauthorised senders using your domain.
In a hosted or managed setup, such as the one provided by DMARC Engine, the aggregate reports are typically collected and analysed automatically, providing you with a centralised view of your email sending activity and authentication results. This can help simplify the process of monitoring and optimising your DMARC configuration, especially for domains with high volume third-party senders.
One of the key challenges when working with aggregate reports is dealing with the sheer volume of data, which can be overwhelming, especially for large domains. To mitigate this, it is essential to implement a robust reporting and analysis system, which can help you filter and prioritise the data, focusing on the most critical issues and trends.
Another critical aspect of aggregate reports is the concept of "other" or "unknown" authentication results, which can indicate that the receiving mail server was unable to verify the authentication status of an email. This can be due to various reasons, such as missing or misconfigured DKIM or SPF records, or issues with the receiving mail server's authentication mechanisms.
In our experience, a significant proportion of aggregate reports contain "other" or "unknown" authentication results, which can make it challenging to accurately assess the effectiveness of your DMARC configuration. To address this, we recommend implementing a comprehensive monitoring and analysis system, which can help you identify and troubleshoot issues with your email sending infrastructure and authentication mechanisms.
When analysing aggregate reports, it is also crucial to consider the reporting period, which can range from a few days to several weeks. This is important, as it can impact the accuracy and relevance of the data, especially for domains with high volume third-party senders.
For instance, if you are reviewing aggregate reports for a domain with a high volume of email sending activity, you may want to focus on reports with a shorter reporting period, such as 24 hours, to get a more accurate picture of the current email sending patterns and authentication results.
In contrast, if you are reviewing aggregate reports for a domain with a lower volume of email sending activity, you may want to focus on reports with a longer reporting period, such as 7 days, to get a more comprehensive view of the email sending patterns and authentication results over time.
Ultimately, the key to optimising DMARC for domains with high volume third-party senders is to carefully analyse the aggregate report data, identifying trends and patterns that can inform your DMARC configuration and email sending infrastructure. By implementing a robust reporting and analysis system, and considering the reporting format, data elements, and reporting period, you can gain valuable insights into your email sending activity and authentication results, and make data-driven decisions to improve the security and deliverability of your emails.
To illustrate this, let us consider a real-world example, where a domain owner noticed a high volume of emails failing DKIM authentication in their aggregate reports. Upon further investigation, they discovered that one of their third-party senders was not correctly configuring the DKIM signature, resulting in a high rate of authentication failures.
By identifying and addressing this issue, the domain owner was able to improve the overall authentication rate for their domain, reducing the risk of email spoofing and improving deliverability. This example highlights the importance of careful analysis and troubleshooting when working with aggregate reports, and the potential benefits of optimising DMARC configuration for domains with high volume third-party senders.
In the next section, we will discuss the process of configuring DMARC for high-volume senders, including the importance of aligning SPF and DKIM records, and the trade-offs between security and deliverability.
Configuring DMARC for High-Volume Senders
When dealing with domains that have a high volume of third-party senders, configuring DMARC effectively is crucial to balance security and deliverability. A common mistake is to set up a DMARC record with a policy that is too restrictive, which can lead to legitimate emails being blocked. For instance, a domain with a high volume of marketing emails sent through a third-party service like Mailchimp or Sendgrid may want to start with a monitoring-only policy, such as p=none, to gather data on email senders and authentication results before moving to a more restrictive policy like p=quarantine or p=reject.
To illustrate this, consider a domain like example.com that uses a hosted DMARC service to manage their DMARC configuration. Their initial DMARC record 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 p=none policy indicates that the domain is only monitoring DMARC authentication results, and not blocking or quarantining emails that fail authentication. The pct=100 tag specifies that the policy should be applied to 100% of emails that fail authentication, and the rua and ruf tags specify the email addresses that should receive aggregate and failure reports, respectively.
As the domain owner gathers more data on their email senders and authentication results, they may want to move to a more restrictive policy. However, this should be done carefully, as a policy that is too restrictive can lead to false positives, where legitimate emails are blocked or quarantined. For example, if the domain owner moves to a p=reject policy without ensuring that all of their third-party senders are authenticating correctly, they may find that a large volume of legitimate emails are being blocked.
To mitigate this risk, it's essential to carefully review the domain's aggregate reports to identify any third-party senders that are not authenticating correctly. This can be done by looking for senders that are reporting a high volume of authentication failures, or by using tools like DMARC analyzers to identify trends and patterns in the data. For instance, a domain might notice that a particular third-party sender is consistently reporting authentication failures, and can use this information to work with the sender to resolve the issue.
In a hosted or managed setup, the DMARC service provider will often provide tools and expertise to help the domain owner configure their DMARC record and interpret their aggregate reports. For example, the provider may offer a dashboard that allows the domain owner to view their aggregate reports in real-time, or provide guidance on how to configure their DMARC record to optimise deliverability and security.
When configuring DMARC for high-volume senders, it's also essential to consider the impact of subdomains. If a domain has a high volume of third-party senders that are using subdomains, the domain owner may want to consider setting up separate DMARC records for each subdomain. This can help to ensure that the domain owner has visibility into authentication results for each subdomain, and can make it easier to identify and resolve issues with specific senders.
For example, a domain like example.com might have a subdomain mail.example.com that is used by a third-party email service. In this case, the domain owner might set up a separate DMARC record for the mail.example.com subdomain, like this:
_dmarc.mail.example.com. IN TXT "v=DMARC1; p=none; pct=100; rua=mailto:dmarc@example.com; ruf=mailto:dmarc@example.com; fo=1"This separate DMARC record allows the domain owner to monitor authentication results for the mail.example.com subdomain independently of the parent domain, which can help to improve deliverability and security.
In short, configuring DMARC for high-volume senders requires a careful balance of security and deliverability. By starting with a monitoring-only policy, gathering data on email senders and authentication results, and carefully reviewing aggregate reports, domain owners can optimise their DMARC configuration to ensure that legitimate emails are delivered while minimising the risk of spam and phishing attacks. Hosted or managed DMARC services can provide valuable tools and expertise to help domain owners configure their DMARC records and interpret their aggregate reports, and considering the impact of subdomains is essential to ensure that the domain owner has visibility into authentication results for all of their email senders.
SPF and DKIM Alignment Considerations
When optimising DMARC for domains with high volume third-party senders, one of the most critical aspects to consider is the alignment of SPF and DKIM. Alignment, in this context, refers to the requirement that the domain name in the From header of an email must match, or be aligned with, the domain name in the SPF or DKIM signature. This is crucial because DMARC relies on either SPF or DKIM alignment to determine the authenticity of an email.
In a typical setup, emails sent by third-party senders may use the domain owner's domain in the From header, but the SPF and DKIM signatures may be set up by the third-party sender themselves. For example, a marketing automation platform sending emails on behalf of a company may use the company's domain in the From header, but the emails are actually sent from the platform's own IP addresses, and signed with the platform's own DKIM key.
To illustrate this, consider a scenario where a company, example.com, uses a marketing platform, marketing-platform.com, to send newsletters. The emails sent by the marketing platform may have a From header like newsletter@example.com, but the SPF record for example.com may not include the marketing platform's IP addresses. In this case, the SPF check would fail, and if the DMARC policy is set to reject emails that fail SPF or DKIM checks, the emails may be rejected by the receiving email server.
example.com. IN TXT "v=spf1 include:marketing-platform.com -all"In the above example, the SPF record for example.com includes the marketing platform's domain, allowing emails sent from the platform's IP addresses to pass the SPF check. However, if the marketing platform uses a subdomain, such as marketing.example.com, in its DKIM signature, the DKIM alignment check would fail, because the domain in the From header (example.com) does not match the domain in the DKIM signature (marketing.example.com).
To resolve this issue, it is essential to ensure that the DKIM signature uses a domain that is aligned with the domain in the From header. One way to achieve this is to use a custom DKIM selector, which allows the domain owner to specify a unique domain for the DKIM signature. For instance, the marketing platform could use a DKIM selector like example-marketing, and the domain owner could configure their DNS to include a TXT record for the selector, like this:
example-marketing._domainkey.example.com. IN TXT "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCqGKukO1De7zhZj6+H0qtjTkVxwTCpvKe4eCZ0FPqri0cb2JZfXJ/DgYSF6vUpwmJG8wVQZKjeGcjDOL5UlsuusFncCzWBQ7RKNUSesmQRMSGkVb1/3j+skZ6UtW+5u09lHNsj6tQ51s1SPrCBkedbNf0Tp0GbMJDyR4e9T04ZZwIDAQAB"In a hosted or managed setup, such as the one provided by DMARC Engine, the process of configuring DKIM selectors and SPF records is often streamlined, allowing domain owners to easily manage their DMARC configuration and ensure alignment between SPF and DKIM. The hosted setup may also provide additional features, such as automated DNS configuration and DKIM key management, to simplify the process of setting up and maintaining DMARC.
When considering SPF and DKIM alignment, it is also essential to take into account the concept of organisational domains. An organisational domain is a domain that is owned and controlled by the same organisation as the domain in the From header. For example, if a company owns both example.com and example.net, and an email is sent from newsletter@example.com with a DKIM signature from example.net, the DKIM alignment check would pass, because example.net is an organisational domain of example.com.
However, if the company uses a third-party sender that is not an organisational domain, such as marketing-platform.com, the DKIM alignment check would fail, unless the third-party sender uses a custom DKIM selector that is aligned with the domain in the From header.
In short, when optimising DMARC for domains with high volume third-party senders, it is crucial to consider the alignment of SPF and DKIM. This involves ensuring that the domain name in the From header matches the domain name in the SPF or DKIM signature, and using custom DKIM selectors and organisational domains to achieve alignment. By taking these considerations into account, domain owners can ensure that their DMARC configuration is optimised for both security and deliverability.
To achieve optimal alignment, it is recommended to use a combination of SPF and DKIM, and to configure the DMARC policy to reject emails that fail either SPF or DKIM checks. Also, domain owners should regularly monitor their DMARC reports to identify any issues with SPF or DKIM alignment, and adjust their configuration as needed to ensure optimal deliverability and security.
By following these best practices, domain owners can ensure that their DMARC configuration is optimised for high volume third-party senders, and that their emails are delivered securely and reliably to the intended recipients.
In terms of specifics, it is recommended to use a DMARC policy that is set to reject emails that fail SPF or DKIM checks, such as p=reject. This policy should be combined with a SPF record that includes all the IP addresses of the third-party senders, and a DKIM signature that uses a custom selector that is aligned with the domain in the From header.
For example, the DMARC record for example.com could be set to:
_dmarc.example.com. IN
## Optimising DMARC Policy for Security and Deliverability
When it comes to optimising DMARC policy for domains with high volume third-party senders, the centre of attention should be on striking a balance between security and deliverability. This is not a straightforward task, as tightening security can often lead to deliverability issues, and vice versa. A key consideration is the `p` parameter in the DMARC record, which defines the policy to be applied to email that fails DMARC validation.
The most common values for the `p` parameter are `none`, `quarantine`, and `reject`. The `none` policy is often used during the initial setup and testing phase, as it allows for monitoring of DMARC validation results without affecting deliverability. However, for domains with high volume third-party senders, using the `none` policy can leave the domain vulnerable to phishing attacks, as malicious emails can still be delivered to recipients.
A more secure approach is to use the `quarantine` or `reject` policy. The `quarantine` policy will flag emails that fail DMARC validation, allowing the receiving email server to quarantine the email, while the `reject` policy will prevent emails that fail DMARC validation from being delivered altogether.
For example, a DMARC record with a `quarantine` policy might look like this:_dmarc.example.com. IN TXT "v=DMARC1; p=quarantine; pct=100; rua=mailto:dmarc@example.com; ruf=mailto:dmarc@example.com; fo=1"
In this example, the `p=quarantine` parameter specifies that emails that fail DMARC validation should be quarantined, and the `pct=100` parameter specifies that the policy should be applied to 100% of emails.
However, when using the `quarantine` or `reject` policy, it is essential to ensure that all legitimate third-party senders are properly configured to pass DMARC validation. This can be a complex task, especially for domains with a large number of third-party senders.
One approach to simplify this process is to use a hosted or managed DMARC setup, which can provide tools and expertise to help configure and manage DMARC for high volume third-party senders. For instance, a managed DMARC service can help to identify and configure legitimate third-party senders, and provide real-time monitoring and alerts to detect any issues with DMARC validation.
Another important consideration when optimising DMARC policy is the `pct` parameter, which specifies the percentage of emails to which the DMARC policy should be applied. Setting the `pct` parameter to 100 will apply the DMARC policy to all emails, while setting it to a lower value, such as 10 or 20, will apply the policy to only a subset of emails.
Using a lower `pct` value can be useful during the initial setup and testing phase, as it allows for monitoring of DMARC validation results without affecting deliverability. However, for domains with high volume third-party senders, using a lower `pct` value can leave the domain vulnerable to phishing attacks, as malicious emails can still be delivered to recipients.
For example, a DMARC record with a `pct` value of 20 might look like this:_dmarc.example.com. IN TXT "v=DMARC1; p=quarantine; pct=20; rua=mailto:dmarc@example.com; ruf=mailto:dmarc@example.com; fo=1"
In this example, the `pct=20` parameter specifies that the DMARC policy should be applied to 20% of emails.
It is also essential to monitor DMARC validation results regularly, to detect any issues with DMARC configuration or third-party sender setup. This can be done by analysing aggregate report data, which provides information on DMARC validation results for emails sent from the domain.
For instance, a hosted or managed DMARC setup can provide real-time monitoring and alerts to detect any issues with DMARC validation, and provide tools to help analyse and troubleshoot DMARC validation results.
In addition to monitoring DMARC validation results, it is also important to monitor email deliverability, to detect any issues with DMARC configuration or third-party sender setup that may be affecting deliverability. This can be done by tracking email delivery rates, bounce rates, and spam complaint rates.
By striking a balance between security and deliverability, and by regularly monitoring DMARC validation results and email deliverability, domains with high volume third-party senders can optimise their DMARC policy to prevent phishing attacks and ensure reliable email deliverability.
In terms of specific recommendations, we suggest starting with a `quarantine` policy and a `pct` value of 100, and then adjusting the `pct` value as needed based on DMARC validation results and email deliverability. We also recommend regularly monitoring DMARC validation results and email deliverability, and using a hosted or managed DMARC setup to simplify the process of configuring and managing DMARC for high volume third-party senders.
For example, the following DMARC record snippet shows a `quarantine` policy with a `pct` value of 100:_dmarc.example.com. IN TXT "v=DMARC1; p=quarantine; pct=100; rua=mailto:dmarc@example.com; ruf=mailto:dmarc@example.com; fo=1"
This record specifies that emails that fail DMARC validation should be quarantined, and that the policy should be applied to 100% of emails.
In a hosted or managed setup, the DMARC record might be configured and managed on behalf of the domain owner, to simplify the process of configuring and managing DMARC for high volume third-party senders.
Ultimately, the key to optimising DMARC policy for domains with high volume third-party senders is to strike a balance between security and deliverability, and to regularly monitor DMARC validation results and email deliverability. By following these best practices, domains with high volume third-party senders can prevent phishing attacks and ensure reliable email deliverability.
To illustrate this point, consider the example of a domain that uses a `reject` policy with a `pct` value of 100, but has not properly configured all legitimate third-party senders to pass DMARC validation. In this scenario, the domain may experience deliverability issues, as legitimate emails from third-party senders may be blocked by the `reject` policy.
On the other hand, a domain that uses a `quarantine` policy with a `pct` value of 100, and has properly configured all legitimate third-party senders to pass DMARC validation, may be able to prevent phishing attacks while also ensuring reliable email deliverability.
In terms of colour coding, a hosted or managed DMARC setup might use a colour-coded system to indicate the status of DMARC validation for each third-party sender, with green indicating that the sender is properly configured to pass DMARC validation, yellow indicating that the sender is not properly configured, and red indicating that the sender is failing DMARC validation.
This can help to simplify the process of monitoring and troubleshooting DMARC validation results, and can provide a clear visual indication of the status of DMARC validation for each third-party sender.
## Monitoring and Adjusting DMARC Configuration
To centre your DMARC configuration around the needs of high volume third-party senders, you must organise a robust monitoring system. This involves regularly reviewing aggregate reports, also known as Reporting Using Aggregated Data (RUA) reports, which provide insights into email authentication results. At DMARC Engine, we handle RUA reports for our customers, and a common issue we see is the lack of attention to these reports, leading to suboptimal DMARC configurations.
When monitoring RUA reports, it is essential to focus on the colour of the authentication results, which indicate whether emails passed or failed DMARC checks. For instance, a report may show a high percentage of emails failing DMARC due to SPF alignment issues. This could be due to a third-party sender not being included in the domain's SPF record. To optimise the DMARC configuration, you would need to add the sender's IP address to the SPF record, as shown in this example:markdown
v=spf1 include:_spf.example.net include:thirdpartysender.com -all
In this example, the SPF record includes the IP addresses of both the domain's own mail server (`_spf.example.net`) and the third-party sender (`thirdpartysender.com`).
Another crucial aspect of monitoring DMARC configuration is adjusting the policy to balance security and deliverability. A common trade-off is between the `none`, `quarantine`, and `reject` policies. While the `reject` policy provides the highest level of security, it may also lead to false positives, where legitimate emails are blocked. On the other hand, the `none` policy may not provide sufficient security, as it only monitors email authentication results without taking any action.
To mitigate this trade-off, we recommend starting with a `none` policy and gradually moving to a `quarantine` or `reject` policy as the domain's DMARC configuration is optimised. This approach allows you to monitor email authentication results, identify potential issues, and adjust the configuration before implementing a more restrictive policy.
In a hosted or managed setup, such as DMARC Engine, the process of monitoring and adjusting DMARC configuration is streamlined. Our platform provides automated RUA report analysis, alerts for potential issues, and recommendations for optimising DMARC configuration. This enables our customers to focus on their core business while ensuring their DMARC configuration is optimised for security and deliverability.
When adjusting DMARC configuration, it is also essential to consider the impact on email deliverability. For instance, adding a new third-party sender to the SPF record may improve deliverability, but it may also increase the risk of spam emails being sent from the domain. To mitigate this risk, we recommend implementing a robust email validation process, such as DKIM signing, to ensure that only authorised senders can send emails on behalf of the domain.
In addition to monitoring RUA reports and adjusting DMARC configuration, it is crucial to keep track of changes to the domain's email infrastructure, such as updates to SPF or DKIM records. This ensures that the DMARC configuration remains aligned with the domain's email setup, preventing potential issues with email deliverability.
To illustrate this point, consider a scenario where a domain updates its DKIM record to use a new selector. If the DMARC configuration is not updated to reflect this change, emails sent using the new selector may fail DMARC checks, leading to deliverability issues. To avoid this, the DMARC configuration should be updated to include the new selector, as shown in this example:markdown
v=DMARC1; p=none; pct=100; rua=mailto:aggregatereports@example.com; ruf=mailto:forensicreports@example.com; adkim=r; aspf=r; fo=1
In this example, the `adkim` tag is set to `r`, which means that the domain is using relaxed DKIM alignment. This allows the domain to use a new DKIM selector without affecting the DMARC configuration.
In short, monitoring and adjusting DMARC configuration is a critical aspect of optimising DMARC for domains with high volume third-party senders. By regularly reviewing RUA reports, adjusting the DMARC policy, and keeping track of changes to the domain's email infrastructure, you can ensure that your DMARC configuration is optimised for both security and deliverability. At DMARC Engine, we provide our customers with the tools and expertise needed to optimise their DMARC configuration, ensuring that their emails are delivered securely and reliably.
## Real-World Examples of DMARC Optimisation
When dealing with domains that have high volume third-party senders, optimising DMARC can be a complex task. One of the key challenges is balancing the need to prevent unauthorised email senders with the need to ensure legitimate emails are delivered. A good example of this is a large e-commerce company that uses a third-party email service provider to send transactional emails to its customers. The company's domain, `example.co.uk`, is set up with a DMARC record that has a policy of `quarantine` to prevent spam emails from being delivered.
markdown
DMARC record for example.co.uk
_dmarc.example.co.uk. IN TXT "v=DMARC1; p=quarantine; pct=100; rua=mailto:aggregate@example.co.uk; ruf=mailto:forensic@example.co.uk; fo=1"
In this example, the `pct=100` tag indicates that the DMARC policy should be applied to 100% of emails that fail DMARC authentication. However, this can cause issues if the third-party email service provider is not properly configured to send emails that pass DMARC authentication. To optimise the DMARC setup for this domain, we would need to adjust the `pct` tag to a lower value, such as `pct=20`, to ensure that only a portion of emails that fail DMARC authentication are quarantined.
Another example is a university domain, `uni.ac.uk`, that has a large number of third-party senders, including student organisations and alumni groups. The university's DMARC record has a policy of `none` to monitor email authentication without blocking or quarantining emails.
markdown
DMARC record for uni.ac.uk
_dmarc.uni.ac.uk. IN TXT "v=DMARC1; p=none; pct=100; rua=mailto:aggregate@uni.ac.uk; ruf=mailto:forensic@uni.ac.uk; fo=1"
To optimise the DMARC setup for this domain, we would need to analyse the aggregate report data to identify the third-party senders that are not authenticating correctly. We can then work with these senders to ensure they are properly configured to send emails that pass DMARC authentication. For example, we may need to add the senders' IP addresses to the university's SPF record or ensure that they are using a valid DKIM key.
In a hosted or managed setup, such as the one provided by DMARC Engine, the process of optimising DMARC is simplified. The platform provides a centralised dashboard for monitoring and managing DMARC configuration, as well as tools for analysing aggregate report data and identifying areas for improvement. For example, the platform may provide a colour-coded system for indicating the authentication status of different senders, with red indicating senders that are not authenticating correctly and green indicating senders that are.
When optimising DMARC for domains with high volume third-party senders, it is also important to consider the impact of SPF and DKIM alignment. For example, if a domain has a strict SPF policy that only allows emails to be sent from a specific set of IP addresses, this may cause issues for third-party senders that are not included in the SPF record. To mitigate this, we can use a more relaxed SPF policy that allows emails to be sent from a wider range of IP addresses.
markdown
SPF record for example.co.uk
example.co.uk. IN TXT "v=spf1 ip4:192.0.2.1 ip4:192.0.2.2 include:_spf.example.net -all"
In this example, the `include:_spf.example.net` tag allows emails to be sent from the IP addresses listed in the `_spf.example.net` record, which may include the IP addresses of third-party senders. However, this can also increase the risk of spam emails being sent from these IP addresses, so it is important to carefully evaluate the trade-offs and ensure that the SPF policy is aligned with the domain's overall security and deliverability goals.
In terms of concrete recommendations, we suggest the following best practices for optimising DMARC for domains with high volume third-party senders:
* Start with a monitoring-only DMARC policy (`p=none`) to gather data on email authentication and identify areas for improvement.
* Analyse aggregate report data to identify third-party senders that are not authenticating correctly and work with these senders to ensure they are properly configured.
* Use a relaxed SPF policy that allows emails to be sent from a wider range of IP addresses, but carefully evaluate the trade-offs and ensure that the SPF policy is aligned with the domain's overall security and deliverability goals.
* Consider using a hosted or managed DMARC platform to simplify the process of monitoring and managing DMARC configuration.
* Regularly review and update the DMARC configuration to ensure it remains aligned with the domain's changing email landscape and security requirements.
By following these best practices and carefully evaluating the trade-offs, organisations can optimise their DMARC setup to prevent unauthorised email senders while ensuring legitimate emails are delivered. This requires a deep understanding of the domain's email ecosystem and the ability to analyse complex data sets, but the benefits to security and deliverability make it well worth the effort.
## Mitigating False Positives and Negatives
When managing DMARC for domains with high volume third-party senders, one of the most critical challenges is mitigating false positives and negatives, which can significantly impact deliverability and security. A false positive occurs when a legitimate email is incorrectly flagged as spam or blocked, while a false negative happens when a spam email is not detected as such. To centre our approach on mitigating these issues, we must delve into the specifics of DMARC configuration, SPF, and DKIM alignment.
In our experience, false positives often arise from overly restrictive DMARC policies or misconfigured SPF records. For instance, a domain with a high volume of third-party senders might set a DMARC policy of `p=reject` without ensuring all senders are properly configured, leading to legitimate emails being rejected. To optimise this, we recommend starting with a monitoring policy of `p=none` and gradually moving to `p=quarantine` or `p=reject` as the domain's senders are validated and aligned.
Consider the example of a domain that uses a hosted DMARC service, which provides a colour-coded dashboard to highlight potential issues. The domain `example.co.uk` has a DMARC record with a policy of `p=quarantine`:markdown
_dmarc.example.co.uk. IN TXT "v=DMARC1; p=quarantine; pct=100; rua=mailto:aggrep@example.co.uk; ruf=mailto:forensics@example.co.uk; fo=1"
In this case, the `pct=100` tag indicates that the policy applies to 100% of emails, which may lead to false positives if not all senders are properly configured. To mitigate this, we can adjust the `pct` tag to a lower value, such as `pct=20`, to apply the policy to only 20% of emails, allowing for a more gradual rollout and reducing the risk of false positives.
SPF alignment is another critical aspect of mitigating false positives and negatives. When a domain has multiple third-party senders, it can be challenging to ensure all senders are included in the SPF record. We recommend using a hosted SPF service that can help manage and optimise SPF records. For example, the domain `example.co.uk` has an SPF record that includes multiple third-party senders:markdown
example.co.uk. IN TXT "v=spf1 include:_spf.google.com include:sendgrid.net include:mailchimp.com -all"
In this case, the `include` mechanism is used to include the SPF records of Google, Sendgrid, and Mailchimp, which are all authorised senders for the domain. However, if one of these senders is not properly configured, it can lead to false negatives. To mitigate this, we can use the `ip4` and `ip6` mechanisms to specify the IP addresses of the authorised senders, rather than relying on the `include` mechanism.
DKIM alignment is also crucial in mitigating false positives and negatives. When a domain has multiple third-party senders, it can be challenging to ensure all senders are using the correct DKIM selectors and keys. We recommend using a hosted DKIM service that can help manage and optimise DKIM keys. For example, the domain `example.co.uk` has a DKIM record with a selector of `selector1`:markdown
selector1._domainkey.example.co.uk. IN TXT "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCqGKukO1De7zhZj6+H0qtjTkVxwTCpvKe4eCZ0FPqri0cb2JZfXJ/DgYSF6vUpwmJG8wVQZKjeGcjDOL5UlsuusFncCzWBQ7RKNUSesmQRMSGkVb1/3j+skZ6UtW+5u09lHNsj6tQ51s1SPrCBkedbNf0Tp0GbMJDyR4e9T04ZZwIDAQAB"
In this case, the `selector1` selector is used to specify the DKIM key, which must be aligned with the domain's DMARC policy. To mitigate false positives and negatives, we can use a hosted DKIM service to rotate the DKIM keys and ensure all senders are using the correct selectors and keys.
In a managed setup, the centre of our approach is to monitor the aggregate reports and adjust the DMARC configuration accordingly. We can use the aggregate reports to identify potential issues, such as false positives and negatives, and adjust the DMARC policy and SPF alignment to mitigate these issues. For example, if we notice a high volume of false positives from a particular sender, we can adjust the SPF record to include the sender's IP addresses or adjust the DMARC policy to a less restrictive setting.
In conclusion is not needed here, rather, to summarise our approach, we must consider the specifics of DMARC configuration, SPF alignment, and DKIM alignment to mitigate false positives and negatives. By using a hosted or managed setup, we can optimise our approach and ensure the domain's emails are delivered securely and efficiently. Our experience has shown that a gradual rollout of DMARC policies, combined with careful management of SPF and DKIM alignment, can significantly reduce the risk of false positives and negatives, and improve overall deliverability and security.
## Best Practices for Long-Term DMARC Management
To centre your organisation's email authentication efforts around DMARC, it is crucial to organise a long-term management strategy that optimises security and deliverability. A key aspect of this is monitoring aggregate report data, which our team at DMARC Engine handles on a daily basis for our customers. We have found that regular review of this data helps identify potential issues before they become major problems, such as a third-party sender's sudden change in mailing patterns that could trigger a spike in false positives.
One best practice is to implement a feedback loop with your third-party senders, ensuring they are aware of any changes in your DMARC configuration or issues that may affect their mailings. This can be as simple as providing them with access to a dashboard that displays their sending statistics and any errors encountered. For instance, we have seen cases where a sender's DKIM signature was not correctly aligned with the domain, causing a significant portion of their emails to fail DMARC validation. By alerting the sender to this issue, they can take corrective action to update their DKIM configuration, thereby improving deliverability.
When configuring DMARC for high-volume senders, it is essential to consider the trade-offs between security and deliverability. A strict DMARC policy can help prevent phishing attacks, but it may also block legitimate emails from third-party senders who are not fully aligned with your domain. To mitigate this risk, we recommend starting with a monitoring-only policy (`p=none`) and gradually increasing the strictness of the policy as you gain confidence in your senders' authentication practices. For example:markdown
_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 a monitoring-only policy that will send aggregate reports to `dmarc@example.com` and failure reports to the same address. The `pct=100` tag indicates that the policy should be applied to 100% of incoming emails.
In a hosted or managed setup, such as the one provided by DMARC Engine, the process of monitoring and adjusting DMARC configuration is streamlined through automated tools and expert analysis. Our team can help customers navigate the complexities of DMARC management, including the analysis of aggregate report data and the implementation of optimised DMARC policies. For instance, we can assist in identifying and mitigating false positives and negatives, which are a common challenge in DMARC management. False positives occur when legitimate emails are incorrectly flagged as spam, while false negatives occur when phishing emails are not detected. By carefully analysing aggregate report data and adjusting the DMARC policy accordingly, we can help minimise the occurrence of these issues.
Another critical aspect of long-term DMARC management is maintaining accurate and up-to-date SPF and DKIM records. This is particularly important for domains with high-volume third-party senders, as incorrect or outdated records can lead to authentication failures and deliverability issues. We recommend regularly reviewing SPF and DKIM records to ensure they are correctly configured and include all authorised senders. For example, an SPF record might include the following snippet:plain
example.com. IN TXT "v=spf1 include:_spf.example.net include:_spf.example.io -all"
``
This record includes two authorised senders, and _spf.example.io`, and specifies that all other senders should be rejected.
To colour outside the lines of traditional DMARC management, consider implementing additional security measures, such as BIMI (Brand Indicators for Message Identification) and MTA-STS (Mail Transfer Agent Strict Transport Security). BIMI allows you to specify a logo that will be displayed in supporting email clients when your emails are authenticated, while MTA-STS helps prevent TLS downgrade attacks by enforcing strict transport security for email transmissions. By combining these technologies with a well-managed DMARC configuration, you can significantly improve the security and deliverability of your emails.
In short, long-term DMARC management requires careful planning, ongoing monitoring, and regular adjustments to optimise security and deliverability. By following best practices, such as implementing a feedback loop with third-party senders, considering the trade-offs between security and deliverability, and maintaining accurate SPF and DKIM records, you can help ensure the authenticity and deliverability of your emails. With the right tools and expertise, including those provided by a hosted or managed setup like DMARC Engine, you can navigate the complexities of DMARC management and improve the overall email authentication posture of your organisation.