554 5.4.14 is a permanent SMTP reply meaning routing loop detected (exchange online). Microsoft explains that by default Exchange stops a mail loop after 20 iterations and sends a bounce. Loops usually come from a configuration error, such as forwarding or connectors that send mail back to where it came from.
What 554 5.4.14 means
Microsoft explains that by default Exchange stops a mail loop after 20 iterations and sends a bounce. Loops usually come from a configuration error, such as forwarding or connectors that send mail back to where it came from.
Common causes
Forwarding between two mailboxes or systems
Most commonMailbox A forwards to B, and B forwards back to A.
Hybrid or connector routing points back to itself
CommonAn outbound connector or MX setting sends mail to the system that just sent it.
The domain is set up wrongly in Microsoft 365
CommonThe domain is Authoritative in one system and Internal Relay in another, or MX points to the wrong place.
How to fix 554 5.4.14
- 1
Read the hops in the bounce
The headers in the bounce show which servers the message passed. Find the two that send it back and forth.
- 2
Remove the loop
Fix the forwarding rule, connector or accepted-domain setting that sends mail back.
- 3
Check MX for the domain
Run an MX lookup to confirm the domain points to the system that should receive its mail.
Confirm your domain is set up correctly
Most delivery failures — permanent or temporary — trace back to authentication or reputation. Run a free EmailHealth check to confirm SPF, DKIM, DMARC, blacklist status, and TLS are all healthy for your sending domain. If you send in volume, free daily monitoring will alert you before a small issue becomes a flood of bounces.