5.4.14 Microsoft bounce: routing loop

What 5.4.14 means

Messages looped between servers more than the set limit (20 iterations by default), so Exchange Online stopped the loop. On-premises Exchange reports 5.4.6 for the same condition.

Message text

Routing loop detected

Common causes of 5.4.14

• Automatic forwarding between two mailboxes or servers
• Mail flow or connector configuration error on the sending or receiving side

How to fix 5.4.14

1. Check mailbox forwarding rules on the sender and recipient mailboxes.
2. Run MX lookup on both domains to check the routing path.

Check your domain

Check the MX records of the recipient domainRuns in your browser; nothing is uploaded.

Have the full bounce message? Paste it into the bounce code lookup and it will match the code and the provider for you. Open the bounce code lookup.

How to read 5.4.14

The second part, 5.4.14, is an enhanced status code (RFC 3463 §2) written class.subject.detail. Class 5 is a Permanent failure (5xx): the command was rejected and the sender should not repeat it unchanged (RFC 5321 §4.2.1; RFC 3463 §2).. Subject 4 is network and routing: a problem reaching or routing to the destination. The detail number refines the subject, and providers may define details of their own, which is why one code can read differently at Gmail, Microsoft and Yahoo.

Do not keep resending the same message: a permanent failure repeats until the cause is fixed. Correct the cause, then send a new message.

Official source: learn.microsoft.com. Last verified 2026-10-20.

Related guides

• How to set up MX records (priorities, null MX, migration)
• MX record points to a CNAME: why it breaks and the fix
• MX host does not resolve: causes and how to fix it

Related codes

• 5.4.4 SMTP: unable to route
• 5.4.1 Microsoft: relay access denied
• 5.4.1 Microsoft: recipient rejected
• 550 5.1.1 Microsoft: bad mailbox address
• 550 5.1.10 Microsoft: recipient not found
• 550 5.5.0 Microsoft: mailbox unavailable

FAQ

All bounce codes