postconf -n
If these fail, check your server’s network settings or switch to a stable DNS provider like Google (8.8.8.8) or Cloudflare (1.1.1.1). 2. Verify Transport Map Consistency
This guide will walk you through the most common causes and the commands you need to get your mail queue moving again. 1. Check for DNS Resolution Failures postconf -n If these fail, check your server’s
An unknown mail transport error frequently happens when a service definition is completely missing or improperly formatted in /etc/postfix/master.cf .
A large number of "unknown mail transport error" instances are rooted in the server's inability to look up the required DNS records. Postfix needs to resolve either the MX record for the recipient's domain or an A record for a specified relayhost. If nsswitch.conf or the local DNS resolver is misconfigured, or if the upstream DNS server is unreachable, the lookup will fail. The error message might then show: Name service error for name=example.com type=MX: Host not found, try again . This is often a transient network issue but can also be a permanent DNS configuration error. Postfix needs to resolve either the MX record
: Use mailq or postqueue -p to see the status of stuck messages. If you’ve fixed the error, you can try to force delivery with postqueue -f .
If you manage a mail server running Postfix, you have likely seen a cryptic message similar to this in your mail log: try again .
Next time you see it, don’t panic. Check the lines above the error. Test the transport. Flush the queue. You’ll likely be back in business within ten minutes.
If you are using a transport_maps file to route specific domains to specific relays or filters, a typo inside that database will break delivery.
mailq
dovecot unix - n n - - pipe flags=DRhu user=vmail argv=/usr/libexec/dovecot/dovecot-lda -f $sender -d $user@$domain -o plugin/quota=maildir:User quota -d