Fixing Gmail 550 5.7.26 Bounce Errors: SPF and DKIM Checklist

Gmail 550 5.7.26 bounce errors usually point to sender authentication failures, so SPF and DKIM should be checked first.

Start by reading the bounce message to see whether SPF or DKIM failed, then verify the domain’s DNS TXT records.

Confirm the SPF policy, the DKIM selector and public key, and whether DNS is managed at the correct nameserver.

After fixing any issues, send a fresh test email to recheck delivery and make sure Gmail accepts it.