Forwarded customer mail is rejected by our filter
On forwarding the original sender's from-domain stays but envelope-from or the sending IP changes. SPF fails and DMARC alignment can't hold. Not a bug, that's how SMTP works. ARC, SRS or a different forwarding pattern fixes it.
Try this first
- 1Check how you forward. Native M365 or Google forwarding rewrites envelope-from (SRS-like) and signs ARC. Server-side is more robust than a client-side rule.
- 2For mailman or legacy lists: use From-rewriting (list becomes sender, original in Reply-To). Not ideal but reliable.
- 3Enable ARC validation on your inbound filter. Defender for O365 does it, Google too. The end recipient can then trust the original pass.
- 4Avoid 'auto-forward to external' as policy where not strictly needed. It breaks more often than it helps.
- 5Document who's forwarded to and why. Often these are old rules from a departed employee.
When to bring us in
If you have formal forwarding needs (old domains, M&A, holding structure), it's worth putting an SMTP relay in between that does ARC or SRS correctly.
See also
- Our emails land in spam for some recipientsAlmost always an SPF, DKIM, or DMARC setting that is wrong or missing, or a sender name that mimics a well-known brand.
- Someone reports receiving phishing emails "from us"Read: spoofing. Someone is abusing your sender name, not necessarily your actual mailbox.
- An email bounces (NDR): delivery failedThe NDR text usually states the exact reason. Reading it is step one.
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