I'm facing a frustrating DMARC issue where both SPF and DKIM show 'pass' in the headers, but DMARC still fails for some of our emails. This problem arises particularly when I check the aggregate reports instead of just individual test messages. After investigation, I suspect the issue stems from alignment rather than authentication.
The mail is sent through a vendor that has SPF passing for their bounce domain and DKIM passing for their signing domain, but the 'From' address is still our own domain. This means technically everything passes, but not for the same domain, which is why DMARC fails. What's puzzling is the inconsistency; some messages align properly when sent directly, but fail when routed through a different service. Different receivers evaluate the alignment in various ways, making testing feel unreliable.
Most guides only mention that SPF or DKIM needs to pass without emphasizing that alignment is the crucial aspect. Before I push for changes from vendors regarding their DKIM signing or set up custom domains, I wanted to find out how others manage this situation. Do you insist on vendors aligning with your domain, or do you loosen DMARC settings during transitions to accommodate some noise?
5 Answers
This is a frequent issue with DMARC in the real world, especially when dealing with multiple vendors. One thing that really helped us was relying more on aggregate reports. They provided insights into alignment failures by source IP and vendor over time, which made it much easier to identify who really needed custom DKIM or a branded return path. Tools like Suped make this process easier by showing alignment issues and vendor-specific problems without the hassle of digging through XML.
Having a clear idea of whose domain you're talking about is key. Are you referring to their actual domain, or a subdomain of yours? Just clarifying that can help streamline troubleshooting.
DMARC alignment is basically the reality check for email authentication! You’ve discovered that having SPF and DKIM pass is only the first step. Many organizations deal with this by initially accepting that it won't work perfectly until they get the vendors to sign with the correct domain or set up subdomains. Gradually, they tighten the DMARC policy from none to quarantine and finally to reject once they have more confidence.
Consider posting in a specialized forum for additional support. Alignment is vital, especially with DKIM. If you're thinking about custom domains for your vendors to send mail as [yourdomain.com](http://yourdomain.com) via DKIM, then yes, that's definitely the route to take.
For the emails to align properly, the 'From' header must be authenticated by your own domain. This means that the vendor's mail server's IP address should be included in your SPF record, and their DKIM needs to be added preferably as a CNAME. Without this alignment, DMARC becomes ineffective. I personally recommend having them use a subdomain, like foo@${vendor}.${your-domain}.com. We went through this last year and aimed to have the vendor's setup sorted before enabling quarantine.
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