5.4.14 Hop count exceeded - possible mail loop ATTR34
Sample bounce line
5.4.14 Hop count exceeded - possible mail loop ATTR34
What it means
A mail loop or routing problem in Exchange Online: the message exceeded the hop count. Exchange Online accepted the message but couldn't route it correctly to the recipient, and Exchange interrupts a loop after 20 iterations and sends an NDR to the sender.
Why it happens
- Accepted domain configuration issues: Exchange Online accepted the message based on the recipient's domain but couldn't correctly route it.
- Hybrid environments: misconfigured connectors in Exchange Online, for example a hybrid connector using DNS routing instead of smart host routing.
- Configuration errors on the sending server, the receiving server, or both, including automatic message forwarding loops.
How to fix it
- Only an Exchange Online admin can usually fix this.
- Verify the recipient's domain is configured as an authoritative accepted domain in Exchange Online.
- Hybrid: use a dedicated connector with smart host routing pointing to the on-premises hybrid server (the easiest fix is to rerun the Hybrid Configuration Wizard), and verify the connector's routing and scope settings.
- Check whether automatic forwarding is enabled in the sender's and recipient's mailbox rules.
Check your domain now
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Related errors
No related errors listed yet.