Put the message on hold to stop the crash loop: postsuper -h QUEUE_ID
"delivery temporarily suspended: unknown mail transport error" in Postfix generally means the system is trying to use a transport service
There is something profoundly unsettling about a non-answer. In human conversation, it’s a shrug. In literature, it’s a blank page. But in the world of system administration, it takes a particularly poetic and maddening form: "delivery temporarily suspended: unknown mail transport error." Put the message on hold to stop the
To force Postfix to clear the suspension flag and immediately retry all deferred and suspended mail, run: postfix flush Use code with caution.
When you see the error delivery temporarily suspended: unknown mail transport error , it means that Postfix has attempted to deliver a message but has encountered an internal problem that prevents it from determining which transport (or how) to use. This is a , which Postfix classifies as a 4.x.x error. It will continue to retry delivery for a period (usually several days) before giving up and returning the message to the sender as undeliverable. But in the world of system administration, it
openssl s_client -connect smtp.sendgrid.net:587 -starttls smtp -crlf
If you are seeing the error "delivery temporarily suspended: unknown mail transport error" in your Postfix mail logs, your email server has stopped sending messages to a specific destination. This error is a generic "catch-all" that indicates Postfix tried to hand off an email to a delivery agent (like SMTP or Dovecot), but the hand-off failed for a reason Postfix doesn't fully understand. It will continue to retry delivery for a
example.com smtp:[://example.com] anotherdomain.com dovecot: Use code with caution.