# For MySQL connect_timeout = 5 timeout = 2 option = 3 # MYSQL_OPT_RECONNECT connect_timeout = 5 keepalive = 1 keepalive_idle = 60
setenforce 0 (temporarily). If the error stops, SELinux is blocking the transport. 5. Postfix Upgrade Inconsistency ("upd" version mismatch) If you recently ran apt upgrade postfix or yum update postfix , old process binaries may linger. You might have a new master.cf but an old upd daemon still running in memory. This mismatch triggers "unknown transport error" because the IPC protocol changed between versions. Step-by-Step Diagnostic Workflow Do not blindly restart services. Follow this forensic approach. Step 1: Isolate the Exact Queue ID Find the specific email causing the error: # For MySQL connect_timeout = 5 timeout =
grep "delivery temporarily suspended" /var/log/maillog | tail -20 You will see a Queue ID (e.g., 3F4A1A0B2C ). Use it to inspect the message: " it is asking you
When Postfix says "unknown," it is asking you, the administrator, to become the detective. Your logs, your postcat output, and your database error logs hold the real answer. to become the detective. Your logs
df -h /var/spool/postfix df -i /var/spool/postfix # Check inode usage dmesg | grep -i "error\|corrupt" A malformed entry in your transport file can cause this. For example: