Separate the two identities#
SMTP login authenticates a client to a submission service. The recipient sees a delivered message and evaluates its own authentication evidence. A correct username and password therefore cannot resolve every sending-domain problem.
Inspect a received message#
Capture the visible From domain, envelope sender and DKIM signing domain. Compare them with the authentication results inserted by your receiving service. A mobile app may use a different sending path from your desktop client, even for the same visible address.
Repair the responsible configuration#
Check the account’s submission host, authorized sender settings and domain setup with the service operator. Re-test using that exact app. Avoid relaxing domain policy until you understand which identity or signing step is wrong.
Primary references
Consult the current specification or provider guidance when applying these checks.
DMARC specification