Known quirk
Postmark's SPF may not line up with your domain
We didn't find a custom return path for Postmark, so its SPF won't line up with your domain. That's normal for Postmark. Your mail is still authenticated, because Postmark signs it with your DKIM key.
What this means for you
- Nothing to change while DKIM keeps signing.
- In DMARC reports, Postmark mail shows SPF not aligned and DKIM aligned. That's expected.
- A custom return path in Postmark (it suggests pm-bounces) lines SPF up too.
If Postmark mail stops signing with DKIM, your report shows it as a gap.
Why it happens
SPF checks the hidden bounce address, not the one people see. Postmark's default bounce address is on its own domain, so SPF can pass without matching yours. DMARC only needs SPF or DKIM to match, and DKIM does.
Technical detail
Postmark's default Return-Path is pm_bounces@pm.mtasv.net, so SPF isn't aligned with the From domain. A custom Return-Path under your domain achieves SPF alignment. DMARC passes through the aligned DKIM signature.
postmark.spf_default_return_path
Sources
Reviewed by healthcheck.email on 2026-10-09.