The short answer is: sometimes. A missing DKIM record on its own might not cause an outright rejection, but it's a major red flag for receiving mail servers. The real risk of rejection comes when you consider DKIM's relationship with another email standard called DMARC.
Fundamentally, DKIM (DomainKeys Identified Mail) acts as a digital signature for your emails. It provides a cryptographic key that receiving servers can use to verify that your email is genuinely from your domain and hasn't been altered in transit. This process is crucial for building trust with mailbox providers like Gmail and Outlook.
Without DKIM, a receiving server has less evidence to prove that your email is legitimate. While this might not lead to an immediate rejection, it can certainly contribute to your message landing in the spam folder.
The critical role of DMARC
The factor that turns a missing DKIM record from a potential problem into a definite cause for rejection is DMARC (Domain-based Message Authentication, Reporting, and Conformance). DMARC is a policy you publish in your DNS records that tells receiving servers what to do with emails that fail authentication checks like SPF and DKIM.
DMARC works on a principle of alignment. For an email to pass DMARC, it must pass either SPF or DKIM, and the domain used for that passing check must align with the domain in the 'From' address the recipient sees. A missing DKIM signature is an automatic DKIM failure. As noted by 101domain's blog, this can be a direct cause of DMARC failure.
Your DMARC policy can specify one of three actions:
- p=none: This is a monitoring policy. The receiving server takes no action but sends reports to you about authentication failures. An email with a missing DKIM record would still be delivered.
- p=quarantine: This policy tells the server to treat failing emails with suspicion, usually by sending them to the spam or junk folder. If your email is missing a DKIM signature and also fails SPF alignment, it will be quarantined.
- p=reject: This is the strictest policy. It instructs the server to completely reject any email that fails DMARC. If your email is missing a DKIM signature and also fails SPF alignment, it will be blocked and will never reach the recipient's inbox.
What happens if I don't have DMARC?
If you have no DMARC policy at all, the decision to reject an email is left entirely up to the receiving mail server's internal rules. In this scenario, a missing DKIM record is just one of many signals the server will evaluate. While it won't guarantee rejection, it will damage your sender reputation and increase the likelihood of your emails being flagged as spam. As AutoSPF points out, a DKIM failure can lead to rejection or delivery to the spam folder, hurting your overall deliverability.
However, with the latest requirements from providers like Google and Yahoo, not having DMARC is becoming less of an option for anyone sending bulk email.
Conclusion: a missing DKIM record is a serious issue
So, does a missing DKIM record lead to rejection? It absolutely can. While it might not be the single cause of a bounce in every situation, its absence is a critical failure in the world of modern email authentication.
At best, a missing DKIM record hurts your sender reputation and deliverability. At worst, when combined with a strict DMARC policy, it guarantees your email will be rejected. Implementing DKIM is a non-negotiable step for anyone serious about email deliverability and protecting their domain from spoofing attacks.
