554: mail loop detected

What it means

A mail loop happens when forwarding rules point back at each other, for example A forwards to B and B forwards to A, so a message circles until something stops it. Case r2101 means GMX detected such a loop. Case r0723 is how it often shows: each pass adds a Received header, and GMX refuses messages with more Received headers than it accepts, assuming a loop. Both are refused with 554. The fix is to correct the forwarding so no chain leads back to where it started.

Common causes

• Two or more mailboxes forward to each other.
• A forward to GMX sends the mail to an address that forwards back to the origin.
• A misconfigured mail server relays mail back to itself.

How to fix it

1. 01List the forwarding rules on every mailbox involved and find the one that closes the loop.
2. 02Remove or change that rule so the chain ends in a mailbox that keeps the mail.
3. 03Look at the Received headers of a bounced message to see the path it took.

Sources

What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.

• GMX Postmaster case r2101: 554 Mail loop suspectedpostmaster.gmx.net
• GMX Postmaster case r0723: 554 Transaction failed (too many Received headers)postmaster.gmx.net

Further reading

• Email headers analyzer