email forwarding

When an email is sent from the sending server, directly to the receiving server, SPF and DKIM  (if set up correctly) authenticate the email normally and usually effectively validate it as legitimate or unauthorized. However, that is not the case if the email passes through an intermediary mail server before it gets delivered to the recipient, such as in the case of forwarded messages. This blog is intended to take you through the impact of email forwarding on DMARC authentication-results.

As we already know, DMARC makes use of two standard email authentication protocols, namely SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail), to validate inbound messages. Let’s discuss them in brief to get a better understanding of how they function before hopping on to how forwarding can affect them.

Sender Policy Framework

SPF is present in your DNS as a TXT record, displaying all the valid sources that are authorized to send emails from your domain. Every email that leaves your domain has an IP address that identifies your server and the email service provider used by your domain that is enlisted within your DNS as an SPF record. The receiver’s mail server validates the email against your SPF record to authenticate it and accordingly marks the email as SPF pass or fail.

DomainKeys Identified Mail

DKIM is a standard email authentication protocol that assigns a cryptographic signature, created using a private key, to validate emails in the receiving server, wherein the receiver can retrieve the public key from the sender’s DNS to authenticate the messages. Much like SPF, the DKIM public key also exists as a TXT record in the DNS of the domain owner.

The Impact of Email Forwarding on Your DMARC Authentication Results

During email forwarding the email passes through an intermediary server before it ultimately gets delivered to the receiving server. Firstly it is important to realize that email forwarding can be done in two ways- either emails can be manually forwarded, which does not affect the authentication results, or it can be automatically forwarded, in which case the authentication procedure does take a hit if the domain doesn’t have the record for the intermediary sending source in their SPF.

Naturally, usually during email forwarding SPF check fails since the IP address of the intermediary server doesn’t match that of the sending server, and this new IP address is usually not included within the original server’s SPF record. On the contrary, forwarding emails usually don’t impact DKIM email authentication, unless the intermediary server or the forwarding entity makes certain alterations in the content of the message.

Note that for an email to pass DMARC authentication, the email would be required to pass either SPF or DKIM authentication and alignment. As we know that SPF inevitably fails during email forwarding, if in case the sending source is DKIM neutral and solely relies on SPF for validation, the forwarded email will be rendered illegitimate during DMARC authentication.

The solution? Simple. You should immediately opt for full DMARC compliance at your organization by aligning and authenticating all inbound messages against both SPF and DKIM!

Achieving DMARC Compliance with PowerDMARC

It is important to note that in order to achieve DMARC compliance, emails need to be authenticated against either SPF or DKIM or both. However, unless the forwarded messages get validated against DKIM, and rely on only SPF for authentication, DMARC will inevitably fail as discussed in our previous section. This is why PowerDMARC helps you achieve complete DMARC compliance by effectively aligning and authenticating emails against both SPF and DKIM authentication protocols. In this way, even if authentic forwarded messages fail SPF, the DKIM signature can be used to validate it as legitimate and the email passes DMARC authentication, subsequently landing into the receiver’s inbox.

Exceptional Cases: DKIM Fail and How to Resolve It?

In certain cases, the forwarding entity may alter the mail body by making adjustments in MIME boundaries, implementation of anti-virus programs, or re-encoding the message. In such cases, both SPF and DKIM authentication fails and legitimate emails do not get delivered.

Incase both SPF and DKIM fail, PowerDMARC is able to identify and display that in our detailed aggregate views and protocols like Authenticated Received Chain can be leveraged by mail servers to authenticate such emails. In ARC, Authentication-Results header can be passed onto the next ‘hop’ in the line of the message delivery, to effectively mitigate authentication issues while email forwarding.

In case of a forwarded message, when the receiver’s email server receives a message that had failed DMARC authentication, it tries to validate the email for a second time, against the provided Authenticated Received Chain for the email by extracting the ARC Authentication-Results of the initial hop, to check whether it was validated to be legitimate before the intermediary server forwarded it to the receiving server.

So sign up with PowerDMARC today, and achieve DMARC compliance at your organization!

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