setenforce 0 (temporarily). If the error stops, SELinux is blocking the transport.
You will see a Queue ID (e.g., 3F4A1A0B2C ). Use it to inspect the message: setenforce 0 (temporarily)
If an update caused the issue:
The error "delivery temporarily suspended unknown mail transport error postfix upd" is a distress signal from the heart of Postfix's routing engine. It rarely means your mail server is permanently broken, but it does indicate a deep-seated inconsistency—usually a dead database connection, a corrupted queue, or a misconfigured transport map. a corrupted queue