Troubleshooting. Decode the bounce. Fix the failure.
10 guides in this section of the Knowledge Base. For the concepts first, start with Learn.
No guide in this section matches that. The other sections are linked above.
Every guide. In one list.
10 guides
Gmail 550 5.7.26: why your mail bounced and how to fix itGmail refused unauthenticated mail; find the source and give it aligned SPF or DKIM.- 550 5.7.1: email rejected per DMARC policy, and how to fix itOn Microsoft 365 it is usually DMARC, but read the text after the code first.
- 550 5.7.23: your mail failed SPF, and how to fix itSPF checked the envelope IP and it was not listed; add the sender, mind the pool.
- SPF PermError: too many DNS lookups, and how to fix itWhat counts toward the 10-lookup cap and how to come back under it.
- Reverse DNS and PTR records: why mail gets rejectedFCrDNS explained, where the PTR record lives, and the Gmail 5.7.25 bounce.
Yahoo 554 5.7.9 and Gmail bulk-sender errors, decodedWhich Yahoo and Gmail codes mean fix authentication and which mean slow down.- DKIM failed (dkim=fail): why your signature did not verifyThe signature did not verify: a changed body, a missing selector, or the wrong key.
- SMTP error codes: how to read an email bounceReply code, enhanced code, and the text after them: which part to trust.
- SPF ~all vs -all: softfail, hardfail, and which to useWhat softfail and hardfail tell a receiver, and why DMARC makes softfail the safer pick.
- DMARC record set up but no reports yet: what to checkReports arrive once a day after the UTC day ends, and what to check when none come.
Start with one domain. See it with your own data.
Free for one domain, no card. Add one DNS record and the first reports usually arrive within a day.