When this error appears, especially in contexts involving update (which deals with rewriting addresses and resolving transports), several systemic issues are likely:
So the "unknown transport error" often means the remote server broke the rules. It might have: When this error appears, especially in contexts involving
But whether the fix is simple or complex, the memory of that error lingers. It stands as a humble monument to the limits of automation. Because sometimes, the system can’t give you a reason. Sometimes, it doesn’t know. And in those moments, all you can do is retry, wait, and remember that even the most deterministic machine can face the genuinely unknown. Because sometimes, the system can’t give you a reason
Look at the "reason" field. It might give a sub-error hidden by the generic message. Look at the "reason" field
Based on your findings:
The error occurs when the main.cf file points to a transport name (e.g., relayhost , default_transport , or transport_maps ) that is not explicitly defined in the master.cf file. Once Postfix encounters this failure multiple times, it suspends further attempts to the affected destination to prevent resource exhaustion.
postqueue -f
