20 September 2026 · DMARC Engine · 31 min read
Introduction to the Complexity of Third-Party Senders
The use of third-party bulk senders, such as email marketing platforms, is a common practice for organisations looking to optimise their email campaigns. However, this practice introduces a level of complexity when it comes to implementing and managing Domain-based Message Authentication, Reporting, and Conformance (DMARC). At DMARC Engine, we have seen firsthand the challenges that arise when trying to navigate the intricacies of third-party senders and DMARC alignment.
One of the primary issues is that third-party senders often have their own mail servers, which can lead to a mismatch in the domain name of the sender and the domain name of the mail server, resulting in DMARC failure. For instance, consider a company like Example Ltd, which uses a third-party email marketing platform, such as Mailchimp, to send newsletters to their subscribers. When Mailchimp sends an email on behalf of Example Ltd, the email may pass through multiple mail servers, each with its own domain name, before reaching the recipient's inbox.
This can cause problems with DMARC validation, as the recipient's mail server may check the domain name of the mail server that sent the email, rather than the domain name of the sender, and find that they do not match. To illustrate this, let's look at a real-world example of a DMARC record:
_dmarc.example.com. IN TXT "v=DMARC1; p=reject; pct=100; rua=mailto:aggrep@example.com; ruf=mailto:forensics@example.com; fo=1"In this example, the DMARC record for the domain example.com specifies that any email that fails DMARC validation should be rejected, and that aggregate reports should be sent to the email address aggrep@example.com. However, if Mailchimp is sending emails on behalf of example.com, and those emails are passing through Mailchimp's mail servers, the domain name of the mail server may be something like mailchimp.net, rather than example.com.
This would cause the email to fail DMARC validation, as the domain name of the mail server does not match the domain name of the sender. To mitigate this issue, it is essential to implement a solution that allows third-party senders to authenticate emails on behalf of the domain owner, while also ensuring that DMARC alignment is maintained.
One approach is to use a hosted or managed DMARC setup, which can provide a centralised platform for managing DMARC records and monitoring email authentication. For example, at DMARC Engine, we provide a hosted DMARC solution that allows customers to manage their DMARC records and monitor email authentication in real-time.
This can help to simplify the process of managing DMARC alignment with third-party senders, and provide greater visibility into email authentication issues. Another approach is to use Authenticated Received Chain (ARC), which provides a mechanism for preserving the authentication results of an email as it passes through multiple mail servers.
By using ARC, it is possible to ensure that the authentication results of an email are preserved, even if the email passes through multiple mail servers with different domain names. For instance, consider the following ARC record:
arc.example.com. IN TXT "v=ARC1; cv=None; a=rsa-sha256; d=example.com; s=selector1; t=1643723400"In this example, the ARC record for the domain example.com specifies the version of ARC being used, as well as the cryptographic algorithm and selector used for signing the email. By using ARC, it is possible to ensure that the authentication results of an email are preserved, even if the email passes through multiple mail servers with different domain names.
However, implementing ARC can be complex, and requires careful consideration of the trade-offs involved. For example, ARC can add additional overhead to email processing, and may require changes to existing email infrastructure.
Therefore, it is essential to carefully evaluate the benefits and drawbacks of implementing ARC, and to consider the specific requirements of your organisation before making a decision. In the next section, we will delve deeper into the specifics of ARC and its role in DMARC alignment, and provide guidance on how to navigate the complexities of third-party senders and DMARC validation.
Understanding ARC and Its Role in DMARC Alignment
When dealing with third-party bulk senders, one of the primary concerns is maintaining DMARC alignment, which can be compromised when emails are forwarded. This is where Authenticated Received Chain (ARC) comes into play, as it provides a mechanism to preserve the authentication results across email forwarding paths. In a hosted or managed setup, such as the one we operate at DMARC Engine, ARC is crucial for ensuring that emails from our customers' domains remain authenticated, even after passing through multiple intermediaries.
To understand how ARC works, let's consider an example. Suppose we have a customer, example.com, that uses a third-party email service provider, esp.example.net, to send marketing emails. When esp.example.net sends an email on behalf of example.com, it may pass through several mail transfer agents (MTAs) before reaching the recipient's inbox. Each of these MTAs may perform authentication checks, such as SPF and DKIM, and if any of these checks fail, the email may be rejected or marked as spam.
Received: from mail.example.com (mail.example.com [192.0.2.1])
by mx.google.com with ESMTPS id p8si3790911ioe.23.2023.02.20.14.30.00
for <recipient@example.net>
(version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128);
Mon, 20 Feb 2023 14:30:00 +0000In this example, the email is received by mx.google.com from mail.example.com, and the authentication results are recorded in the Authentication-Results header. However, if this email is then forwarded to another recipient, the authentication results may be lost, causing the email to fail DMARC validation.
This is where ARC comes in. By adding an ARC signature to the email, the originating domain can ensure that the authentication results are preserved across the forwarding path. The ARC signature is based on the authentication results of the previous hop, and it is added to the email as an ARC-Seal header.
ARC-Seal: i=1; s=arc.example.com; d=example.com; cv=none;
a=rsa-sha256; t=1645366200;
b=VGVzdCBzdGF0ZW1lbnQgdG8gdGhlIGFydGlmY2l0ZS4KIn this example, the ARC-Seal header indicates that the email has been sealed with an ARC signature, which is based on the authentication results of the previous hop. The cv=none parameter indicates that this is the first hop in the ARC chain.
When the email is forwarded, each subsequent MTA can add its own ARC signature to the email, creating a chain of authentication results. This allows the receiving MTA to verify the authenticity of the email, even if it has passed through multiple intermediaries.
ARC-Authentication-Results: i=2;
s=mx.google.com; d=example.com;
cv=fail; a=rsa-sha256;
t=1645366200;
b=VGVzdCBzdGF0ZW1lbnQgdG8gdGhlIGFydGlmY2l0ZS4KIn this example, the ARC-Authentication-Results header indicates that the email has failed authentication at the mx.google.com MTA. However, because the ARC signature is present, the receiving MTA can still verify the authenticity of the email, based on the authentication results of the previous hop.
In a hosted or managed setup, such as the one we operate at DMARC Engine, ARC is configured automatically for our customers' domains. This involves generating an ARC key pair and adding the ARC-Seal header to outgoing emails. We also configure our customers' domains to use ARC validation, which involves verifying the ARC signature on incoming emails. By using ARC, we can ensure that our customers' emails remain authenticated, even when passing through multiple intermediaries.
One of the key trade-offs to consider when implementing ARC is the added complexity of managing ARC keys and signatures. In a hosted or managed setup, this complexity is handled automatically, but in a self-managed setup, the domain owner must manage the ARC keys and signatures themselves. This can be time-consuming and requires a good understanding of email authentication protocols.
Another consideration is the impact of ARC on email deliverability. Because ARC allows emails to be authenticated even after passing through multiple intermediaries, it can improve email deliverability in some cases. However, it can also lead to increased spam filtering, if the ARC signature is not properly validated. To mitigate this risk, it is essential to configure ARC validation correctly and to monitor email deliverability closely.
In short, ARC is a powerful tool for maintaining DMARC alignment in the presence of third-party bulk senders. By preserving the authentication results across email forwarding paths, ARC can improve email deliverability and reduce the risk of spam filtering. However, it requires careful configuration and management, particularly in self-managed setups. As a hosted or managed setup, we recommend that our customers use ARC to ensure that their emails remain authenticated, even when passing through multiple intermediaries.
The Impact of Forwarding Chains on DMARC Validation
The centre of the problem with DMARC validation and third-party bulk senders lies in the colour of the forwarding chains that emails often pass through. When an email is forwarded, the original alignment between the domain in the From header and the domain in the SPF or DKIM signature can be lost, leading to DMARC validation failures. This is particularly problematic for organisations that rely heavily on third-party senders, as the forwarding chains can introduce multiple layers of complexity.
To illustrate this, consider an example where a company, let's call it example.com, uses a third-party email marketing service, mailer.net, to send newsletters to their subscribers. The email marketing service may use its own domain, mailer.net, in the Return-Path header for bounce handling, while the From header still shows example.com. If the email is then forwarded by a recipient to another email address, the forwarding mail server may modify the headers, potentially breaking the DMARC alignment.
In a hosted or managed setup, such as the one we operate at DMARC Engine, we often see customers struggling to optimise their DMARC configurations to account for these forwarding chains. A common mistake is to overlook the impact of forwarding on DMARC validation, assuming that the use of ARC (Authenticated Received Chain) can simply resolve the issue. While ARC does provide a mechanism to preserve the authentication results across forwarding chains, its implementation and configuration require careful consideration.
One of the key challenges with forwarding chains is the potential for header modification. When an email is forwarded, the forwarding mail server may add or modify headers, which can affect the DMARC validation process. For instance, the Received header may be added or modified, which can change the domain that is used for DMARC validation. To mitigate this, it is essential to carefully configure the DMARC policy and ensure that the third-party sender is using a valid domain in the From header.
A real-world example of this can be seen in the following DMARC aggregate report snippet:
<feedback>
<record>
<row>
<source_ip>192.0.2.1</source_ip>
<count>10</count>
<policy_evaluated>
<disposition>none</disposition>
<dkim>fail</dkim>
<spf>fail</spf>
</policy_evaluated>
</row>
<identifiers>
<header_from>example.com</header_from>
</identifiers>
<auth_results>
<dkim>
<domain>mailer.net</domain>
<result>fail</result>
</dkim>
<spf>
<domain>mailer.net</domain>
<result>fail</result>
</spf>
</auth_results>
</record>
</feedback>In this example, the email was sent by mailer.net on behalf of example.com, but the DMARC validation failed due to the forwarding chain. The dkim and spf results show fail, indicating that the authentication failed.
To address this issue, organisations can use ARC to preserve the authentication results across forwarding chains. ARC provides a mechanism to attach an authentication result to the email, which can be verified by the receiving mail server. However, the implementation of ARC requires careful configuration, including the setup of ARC keys and the configuration of the mail servers to use ARC.
In our experience, the key to successful ARC implementation is to ensure that the third-party sender is configured to use ARC and that the organisation's mail servers are configured to verify the ARC signatures. This requires close collaboration between the organisation and the third-party sender, as well as careful testing to ensure that the ARC implementation is working correctly.
Another important consideration is the impact of forwarding chains on the DMARC policy. When an email is forwarded, the DMARC policy may be evaluated multiple times, which can lead to conflicting results. To mitigate this, organisations can use a DMARC policy that is specifically designed to handle forwarding chains, such as a policy that uses the p tag to specify the DMARC policy for the domain.
In conclusion to this section, the impact of forwarding chains on DMARC validation is a complex issue that requires careful consideration and configuration. By understanding the challenges of forwarding chains and using ARC to preserve authentication results, organisations can optimise their DMARC configurations to ensure successful validation, even in the presence of third-party bulk senders. In the next section, we will provide operational guidance for configuring ARC with third-party senders, including specific recommendations for implementing ARC in a hosted or managed setup.
Operational Guidance for Configuring ARC with Third-Party Senders
Configuring ARC with third-party senders requires careful planning and execution to ensure seamless DMARC alignment and prevent email delivery issues. At DMARC Engine, we have worked with numerous customers to implement ARC with their third-party senders, and we have identified several key considerations to keep in mind.
Firstly, it is essential to understand the different types of third-party senders and their respective requirements for ARC configuration. For example, email service providers (ESPs) like Mailchimp or Sendgrid typically have built-in support for ARC, whereas custom applications or in-house email systems may require manual configuration. In the case of ESPs, the configuration process usually involves adding a few lines of code to the email template or setting up a specific authentication protocol.
For instance, when using Mailchimp, you can add an ARC seal to your emails by including the following code snippet in your email template:
ARC-Seal: i=1; s=mailchimp; d=example.com; cv=none;
a=rsa-sha256; t=1643723900;
b=IGKoSGqyPcUu6XpqjI6YrQZke0zjL9i9zVb7Lp5kF4E=;On the other hand, custom applications or in-house email systems may require a more complex setup, involving the generation of public-private key pairs and the configuration of an ARC signing algorithm.
When configuring ARC with third-party senders, it is crucial to ensure that the sender's domain is properly aligned with the ARC seal. This can be achieved by setting up an ARC validation protocol, such as the ARC-Authentication-Results header, which verifies the authenticity of the ARC seal.
For example, the following ARC-Authentication-Results header snippet indicates that the ARC seal has been successfully validated:
ARC-Authentication-Results: i=1;
auth=pass (arc=true dkim=true spf=pass)
smtp.mailfrom=example.comIn a hosted or managed setup, such as the one offered by DMARC Engine, the configuration process is often simplified through the use of pre-built templates and automated validation protocols. However, it is still essential to carefully review and test the configuration to ensure that it meets the specific requirements of your organisation.
Another critical aspect of configuring ARC with third-party senders is the management of forwarding chains. Forwarding chains can break DMARC alignment, causing emails to be rejected or marked as spam. To mitigate this issue, it is recommended to implement a forwarding protocol, such as SMTP, that preserves the original email headers and ARC seal.
For instance, the following email header snippet shows an example of a preserved ARC seal after forwarding:
Received: from example.com (example.com [192.0.2.1])
by forwarder.example.net (Postfix) with ESMTP id 4D861B00194
for <recipient@example.net>; Fri, 11 Feb 2022 14:30:00 +0000 (GMT)
ARC-Seal: i=1; s=example; d=example.com; cv=none;
a=rsa-sha256; t=1643723900;
b=IGKoSGqyPcUu6XpqjI6YrQZke0zjL9i9zVb7Lp5kF4E=;In addition to preserving the ARC seal, it is also essential to ensure that the forwarding protocol is properly configured to handle email authentication protocols, such as SPF and DKIM. This can be achieved by setting up a forwarding server that is capable of rewriting the email headers and preserving the authentication protocols.
In terms of specific configuration recommendations, we advise customers to use a minimum of two ARC seals, with the first seal being applied by the original sender and the second seal being applied by the forwarding server. This approach helps to ensure that the email remains authenticated throughout the forwarding chain.
For example, the following ARC seal snippet shows an example of a double-sealed email:
ARC-Seal: i=1; s=example; d=example.com; cv=none;
a=rsa-sha256; t=1643723900;
b=IGKoSGqyPcUu6XpqjI6YrQZke0zjL9i9zVb7Lp5kF4E=;
ARC-Seal: i=2; s=forwarder; d=example.net; cv=none;
a=rsa-sha256; t=1643723901;
b=JG61GqyPcUu6XpqjI6YrQZke0zjL9i9zVb7Lp5kF4E=;Also, it is recommended to use a secure protocol, such as HTTPS, to protect the email content and prevent tampering.
In a real-world example, we worked with a large e-commerce company that was experiencing issues with email delivery due to broken DMARC alignment. By implementing ARC with their third-party senders and configuring a secure forwarding protocol, we were able to improve their email deliverability and reduce the risk of email spoofing.
To optimise the configuration process, we recommend using automated tools and scripts to generate and manage ARC seals, as well as to monitor email authentication protocols.
For instance, the following script snippet shows an example of a Python script that generates an ARC seal:
import hashlib
import hmac
def generate_arc_seal(private_key, email_content):
# Generate the ARC seal
arc_seal = hmac.new(private_key, email_content, hashlib.sha256)
return arc_seal.hexdigest()In addition to using automated tools, it is also essential to regularly review and update the ARC configuration to ensure that it remains aligned with the organisation's email authentication protocols and security policies.
In a hosted or managed setup, such as the one offered by DMARC Engine, the configuration process is often simplified through the use of pre-built templates and automated validation protocols. However, it is still essential to carefully review and test the configuration to ensure that it meets the specific requirements of your organisation.
For example, DMARC Engine provides a range of pre-built templates and automated tools to simplify the configuration process, including a template for generating ARC seals and a tool for monitoring email authentication protocols.
In conclusion to this section, configuring ARC with third-party senders requires careful planning and execution to ensure seamless DMARC alignment and prevent email delivery issues. By following the recommendations outlined in this section, organisations can improve their email deliverability, reduce the risk of email spoofing, and maintain a high level of email authentication and security.
To centre the configuration process around the specific needs of your organisation, it is essential to carefully review and test the configuration, as well as to regularly update and refine it to ensure that it remains aligned with your email authentication protocols and security policies.
By taking a proactive and informed approach to configuring ARC with third-party senders, organisations can optimise their email deliverability, improve their online reputation, and reduce the risk of email-based threats.
Case Study: Implementing ARC for a Large-Scale Email Marketing Campaign
Implementing ARC for a large-scale email marketing campaign requires careful planning and consideration of the complexities involved. A recent campaign we worked on at DMARC Engine involved a well-known retail company that wanted to send out a promotional email to their subscribers. The campaign was to be sent by a third-party email marketing service, which would be sending emails on behalf of the retail company. The retail company had already implemented DMARC with a policy of quarantine, and they wanted to ensure that the emails sent by the third-party service would be delivered to the recipients' inboxes without being blocked by DMARC checks.
The first step was to set up an ARC (Authenticated Received Chain) seal on the emails sent by the third-party service. This involved generating a private key and a selector, which would be used to create the ARC signature. The third-party service would then include this signature in the email headers.
ARC-Seal: i=1; a=rsa-sha256; t=1643723400; cv=none;
d=example.net; s=selector1;
b=AjR5jZ4NnQ4N4MzY2MjYzZTM0NGUwNjQ1NjY3ODcyNTU2NjU3MjY1NDU0NDU0NDU0NDU0NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ1NDQ
## Navigating the Trade-Offs of ARC and DMARC Alignment
When implementing ARC (Authenticated Received Chain) to improve DMARC alignment with third-party bulk senders, organisations must carefully consider the trade-offs involved. One of the primary concerns is the potential for ARC to introduce additional complexity into the email authentication process, which can lead to issues with deliverability if not properly managed. For instance, if a third-party sender is using a mail server that does not support ARC, or is not correctly configured to handle ARC headers, this can result in authentication failures and negatively impact deliverability.
A key consideration is the alignment of DMARC policies with ARC. In a hosted or managed setup, such as the one we operate at DMARC Engine, we often see customers struggle with configuring DMARC policies that are too restrictive, which can lead to legitimate emails being flagged as spam or rejected by recipient mail servers. To mitigate this, we recommend a phased approach to implementing DMARC, starting with a monitoring-only policy (p=none) and gradually moving to a more restrictive policy (p=quarantine or p=reject) as the organisation gains more insight into its email authentication landscape.
The following is an example of a DMARC record that is commonly used in our hosted setup:markdown
_dmarc.example.com. IN TXT "v=DMARC1; p=none; pct=100; rua=mailto:aggregate@example.com; ruf=mailto:forensic@example.com; fo=1"
In this example, the `p=none` policy indicates that the organisation is only monitoring DMARC authentication results, and not actively enforcing a policy. The `pct=100` tag specifies that 100% of emails should be subject to DMARC authentication, and the `rua` and `ruf` tags define the email addresses that will receive aggregate and forensic reports, respectively.
When implementing ARC, it is essential to consider the impact on DMARC alignment. ARC allows a mail server to validate the authenticity of an email by verifying the chain of custody, which can help to mitigate issues with DMARC alignment caused by forwarding chains. However, ARC also introduces additional headers into the email, which can potentially cause issues with email clients or mail servers that are not configured to handle these headers correctly.
To illustrate this, consider the following example of an ARC header:markdown
ARC-Seal: i=1; s=example; d=example.com; cv=none;
b=VGVzdCBFbWFpbCBTZXJ2aWNlIGRvZXMgd29ya2xvY2FsIG9uIHRoaXMgaGVhZGVy;
bh=SGVsbG8gd29ybGQh
In this example, the `ARC-Seal` header contains a digital signature that verifies the authenticity of the email. However, if the recipient mail server is not configured to handle ARC headers correctly, this can result in authentication failures or other issues with deliverability.
In our experience, one of the most common issues with ARC implementation is the failure to properly configure the ARC seal. This can result in a situation where the ARC seal is not correctly validated, which can lead to DMARC authentication failures. To avoid this, we recommend carefully testing ARC implementation to ensure that the ARC seal is correctly configured and validated.
Another important consideration is the impact of ARC on email forwarding chains. When an email is forwarded, the ARC headers are typically added to the email, which can help to maintain DMARC alignment. However, if the forwarding mail server is not configured to handle ARC headers correctly, this can result in authentication failures or other issues with deliverability.
To mitigate this, we recommend working closely with third-party senders to ensure that they are correctly implementing ARC and DMARC alignment. This may involve providing guidance on configuring ARC headers, as well as monitoring DMARC authentication results to identify any issues with alignment.
In terms of specific recommendations, we suggest the following:
* Implement a phased approach to DMARC, starting with a monitoring-only policy and gradually moving to a more restrictive policy as the organisation gains more insight into its email authentication landscape.
* Carefully test ARC implementation to ensure that the ARC seal is correctly configured and validated.
* Work closely with third-party senders to ensure that they are correctly implementing ARC and DMARC alignment.
* Monitor DMARC authentication results to identify any issues with alignment, and adjust the DMARC policy as needed to maintain optimal deliverability.
By following these recommendations and carefully navigating the trade-offs involved with ARC and DMARC alignment, organisations can help to ensure optimal deliverability and maintain the trust and integrity of their email communications. In a hosted or managed setup, such as the one we operate at DMARC Engine, we can provide additional guidance and support to help organisations implement ARC and DMARC alignment correctly, and maintain optimal deliverability for their email communications.
## Analyzing Aggregate Reports for Insights into Forwarding Chains
Analyzing aggregate reports is a crucial step in understanding the impact of forwarding chains on DMARC validation. As a senior email-deliverability engineer, I can attest that these reports provide a wealth of information on how emails are being forwarded and validated across different networks. In a hosted or managed setup, such as the one we have at DMARC Engine, we receive these reports from our customers' domains, which enables us to identify potential issues and optimise their DMARC configurations.
When analysing aggregate reports, it is essential to look for forwarding chains, which can be identified by the presence of multiple `Authentication-Results` headers in the report. These headers indicate the authentication results for each hop in the forwarding chain. For instance, consider the following report snippet:markdown
Authentication-Results:
sender=example.com;
spf=pass (ip1: 192.0.2.1)
smtp.mailfrom=example.com;
dkim=pass (sel1:_domainkey.example.com)
header.d=example.com;
dmarc=pass
Authentication-Results:
sender=forwarder.net;
spf=fail (ip2: 198.51.100.1)
smtp.mailfrom=example.com;
dkim=pass (sel1:_domainkey.example.com)
header.d=example.com;
dmarc=fail
In this example, the email was initially sent from `example.com` and then forwarded to `forwarder.net`. The first `Authentication-Results` header shows that the email passed SPF, DKIM, and DMARC validation when it was sent from `example.com`. However, when the email was forwarded to `forwarder.net`, the SPF validation failed, causing the DMARC validation to fail as well.
To gain insights into forwarding chains, it is vital to monitor these reports regularly and look for patterns or anomalies. For instance, if we notice that a particular forwarder is consistently causing DMARC validation failures, we may need to adjust our ARC configuration or work with the forwarder to ensure that they are properly authenticating emails. In a hosted setup, we can automate this process by setting up alerts and notifications for specific types of failures or anomalies.
Another important aspect to consider when analysing aggregate reports is the impact of ARC (Authenticated Received Chain) on DMARC validation. ARC is a protocol that allows intermediate forwarders to attach their authentication results to the email, enabling the receiving domain to verify the authenticity of the email. When ARC is properly implemented, it can help to mitigate the effects of forwarding chains on DMARC validation. However, if ARC is not correctly configured, it can lead to false positives or false negatives, which can compromise the security of the email ecosystem.
To illustrate this point, consider the following example:markdown
ARC-Seal: i=1;
a=rsa-sha256;
cv=none;
d=example.com;
s=arcselector;
t=1643723900;
b=...
ARC-Authentication-Results:
sender=example.com;
spf=pass (ip1: 192.0.2.1)
smtp.mailfrom=example.com;
dkim=pass (sel1:_domainkey.example.com)
header.d=example.com;
dmarc=pass
In this example, the sending domain `example.com` has implemented ARC, which allows the intermediate forwarder to attach its authentication results to the email. The `ARC-Seal` header indicates that the email has been sealed with a digital signature, and the `ARC-Authentication-Results` header shows the authentication results for the email. If the receiving domain trusts the ARC seal, it can use this information to verify the authenticity of the email, even if the email has been forwarded through multiple intermediate forwarders.
In a hosted or managed setup, we can optimise the ARC configuration to ensure that it is properly aligned with the DMARC policy. This may involve setting up ARC validators, configuring ARC sealers, and monitoring ARC-related errors or anomalies. By doing so, we can help our customers to maintain a high level of email deliverability and security, even in the presence of complex forwarding chains.
In addition to analysing aggregate reports, it is also essential to monitor the DMARC policy itself and adjust it as needed. For instance, if we notice that a particular domain is consistently failing DMARC validation due to forwarding chains, we may need to adjust the DMARC policy to allow for more flexibility in the authentication process. This could involve setting up a more permissive DMARC policy, such as `p=none`, or implementing a custom authentication mechanism that takes into account the specific requirements of the domain.
In conclusion to this section, analysing aggregate reports is a critical step in understanding the impact of forwarding chains on DMARC validation. By monitoring these reports regularly and looking for patterns or anomalies, we can gain valuable insights into the email ecosystem and optimise our DMARC configurations to ensure a high level of email deliverability and security. In a hosted or managed setup, we can automate this process and provide our customers with detailed analytics and recommendations to help them navigate the complexities of DMARC and ARC.
## Real-World Examples of DMARC and ARC Record Configurations
When dealing with third-party bulk senders, the configuration of DMARC and ARC records can be a complex task, requiring careful consideration of the trade-offs involved. A key aspect of this is understanding how different record configurations can impact the deliverability of emails. For instance, a common mistake is setting up a DMARC record with a policy of `p=reject` without properly configuring ARC, which can lead to legitimate emails being rejected by receivers.
To illustrate this, consider a company like Example Ltd, which uses a hosted DMARC service to manage their email authentication. Their DMARC record might look like this:markdown
_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 indicates that the company is monitoring email authentication results but not yet enforcing a rejection policy. The `rua` and `ruf` tags specify the email addresses to which aggregate and forensic reports should be sent, respectively.
Now, let's consider how Example Ltd might configure ARC records for their third-party bulk senders. ARC, or Authenticated Received Chain, is a protocol that allows email receivers to verify the authenticity of emails that have been forwarded through multiple hops. When properly configured, ARC can help to prevent legitimate emails from being rejected due to DMARC alignment issues.
For example, suppose Example Ltd uses a third-party email service provider called BulkSender Inc to send marketing emails. BulkSender Inc might have its own ARC record configured as follows:markdown
_arc.bulkSender.com. IN TXT "v=ARC1; cv=none; a=rsa-sha256; d=bulkSender.com; s=selector1"
In this example, the `cv=none` tag indicates that BulkSender Inc is not using a specific validation mechanism for ARC. The `a=rsa-sha256` tag specifies the algorithm used for signing ARC headers, while the `d` and `s` tags specify the domain and selector used for the ARC signature.
When Example Ltd sends emails through BulkSender Inc, the ARC record will be used to verify the authenticity of the emails as they pass through the forwarding chain. The hosted DMARC service used by Example Ltd can help to optimise the configuration of ARC records for their third-party senders, ensuring that emails are properly authenticated and delivered to recipients.
However, there are trade-offs to consider when configuring ARC records. For instance, using a `cv=none` policy can make it more difficult to detect and prevent email spoofing attacks. On the other hand, using a more restrictive validation mechanism can help to improve email security but may also increase the risk of false positives.
To mitigate these risks, it's essential to carefully monitor aggregate reports and adjust the configuration of DMARC and ARC records as needed. For example, Example Ltd might receive an aggregate report that looks like this:markdown
{
"version": 1,
"report_metadata": {
"org_name": "Example Ltd",
"email": "aggrep@example.com",
"extra_contact_info": "",
"report_id": "1234567890",
"date_range": {
"begin": 1643723400,
"end": 1646315200
}
},
"policy_published": {
"domain": "example.com",
"adkim": "r",
"aspf": "r",
"p": "none",
"sp": "none",
"pct": 100
},
"records": [
{
"row": {
"source_ip": "192.0.2.1",
"count": 100,
"disposition": "none",
"dkim": "pass",
"spf": "pass",
"reason": {
"type": "forwarded",
"comment": "ARC signature verified"
}
}
}
]
}
This report indicates that 100 emails were sent from the IP address `192.0.2.1` and were authenticated using both DKIM and SPF. The `reason` field indicates that the emails were forwarded and that the ARC signature was verified.
By analysing these reports and adjusting the configuration of DMARC and ARC records accordingly, organisations like Example Ltd can help to ensure that their emails are properly authenticated and delivered to recipients, while also preventing email spoofing attacks. The key is to strike a balance between email security and deliverability, and to continually monitor and optimise the configuration of DMARC and ARC records to achieve this balance.
In a hosted or managed setup, the centre of attention should be on the optimisation of these records, to ensure that the colour of the email authentication results is always green, indicating a pass. This can be achieved by carefully considering the configuration of DMARC and ARC records, and by continually monitoring aggregate reports to identify areas for improvement.
Ultimately, the goal is to create a robust email authentication system that can help to prevent email spoofing attacks, while also ensuring that legitimate emails are delivered to recipients. By following best practices and carefully configuring DMARC and ARC records, organisations can help to achieve this goal and improve the overall security and deliverability of their emails.
In terms of specifics, it is recommended that organisations use a `p=none` policy for their DMARC records, at least initially, to monitor email authentication results without enforcing a rejection policy. They should also configure ARC records for their third-party bulk senders, using a `cv=none` policy if necessary, to verify the authenticity of emails as they pass through the forwarding chain.
By taking a careful and considered approach to the configuration of DMARC and ARC records, organisations can help to ensure that their emails are properly authenticated and delivered to recipients, while also preventing email spoofing attacks. This requires a deep understanding of the trade-offs involved and a commitment to continually monitoring and optimising the
## Best Practices for Maintaining DMARC Alignment Across Third-Party Senders
Maintaining DMARC alignment across third-party senders is crucial to prevent email spoofing and ensure that emails are delivered to the intended recipients. One of the key challenges is ensuring that the third-party senders are configured correctly to use ARC (Authenticated Received Chain) or other authentication mechanisms. In our experience, a well-organised and centralised approach to managing third-party senders is essential to maintain DMARC alignment.
To start with, it is vital to have a clear understanding of the third-party senders that are being used to send emails on behalf of your organisation. This includes email marketing platforms, customer relationship management (CRM) systems, and other services that may send emails to your customers or users. For each third-party sender, you should have a clear record of their configuration, including their SPF, DKIM, and DMARC records. For example, a typical DMARC record for a third-party sender may look like this:markdown
_dmarc.example.com. IN TXT "v=DMARC1; p=reject; pct=100; rua=mailto:dmarc@example.com; ruf=mailto:dmarc@example.com; fo=1"
In a hosted or managed setup, such as the one we provide at DMARC Engine, this process is simplified through the use of a centralised dashboard that allows you to manage all your third-party senders in one place. Our system also provides automated tools to help you configure and optimise your DMARC records for each sender.
Another best practice is to implement a robust monitoring and reporting system to track DMARC alignment issues. This includes setting up aggregate reports (RUA) to receive daily reports on DMARC validation results from email receivers such as Gmail and Yahoo. These reports provide valuable insights into DMARC alignment issues and can help you identify problems with third-party senders. For instance, a sample RUA report may show the following data:json
{
"report_metadata": {
"org_name": "example.com",
"email": "dmarc@example.com",
"extra_contact_info": "https://example.com/dmarc",
"report_id": "1234567890",
"date_range": {
"begin": "2022-01-01",
"end": "2022-01-01"
}
},
"policy_published": {
"domain": "example.com",
"adkim": "r",
"aspf": "r",
"p": "reject",
"sp": "reject",
"pct": "100"
},
"record": [
{
"row": {
"source_ip": "192.0.2.1",
"count": "10",
"disposition": "none",
"dkim": "pass",
"spf": "pass"
}
},
{
"row": {
"source_ip": "198.51.100.1",
"count": "5",
"disposition": "quarantine",
"dkim": "fail",
"spf": "fail"
}
}
]
}
By analysing these reports, you can identify issues with third-party senders and take corrective action to maintain DMARC alignment.
In addition to monitoring and reporting, it is also essential to have a process in place for onboarding new third-party senders. This includes providing them with clear guidelines on how to configure their SPF, DKIM, and DMARC records to maintain DMARC alignment. We recommend that you provide a standardised template for third-party senders to use, which includes the required DMARC record and any other necessary configuration settings. For example, you may provide a template like this:markdown
SPF record: v=spf1 include:thirdparty.example.com -all
DKIM record: k1._domainkey.example.com. IN TXT "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCqGKukO1CrA48bQjoi8YErODUsQQtp+jiiMdAKTzxNr2Ym4W8Jo7+qwIXnvVv4ZaHvGqoY8RV/1VZ4HvRZZtIy8duq6Bbi0Ly3haEqX2a14dkpXGv2PbUYGqfRIZUVeJAVq4On6qj3jy/12bX6VL0KE18k8ApeL04vWNDu+DcUwIDAQAB"
DMARC record: _dmarc.example.com. IN TXT "v=DMARC1; p=reject; pct=100; rua=mailto:dmarc@example.com; ruf=mailto:dmarc@example.com; fo=1"
```
By providing a standardised template and clear guidelines, you can ensure that new third-party senders are configured correctly and that DMARC alignment is maintained.