Delivery Temporarily Suspended Unknown Mail Transport Error Postfix Upd 2021 [HD 2027]

On Red Hat/CentOS:

Ensure that smtp_sasl_password_maps points to a valid and hashed SASL password file, and that the password is correct for the provider.

: If you use a transport table, check for typos in the service names (e.g., writing instead of default_transport : Ensure this is set to a valid service defined in your Red Hat Customer Portal 2. Verify Service Definitions in Postfix looks for transport names in /etc/postfix/master.cf . If your config mentions a transport like private/filter , that exact name must have an entry in Server Fault /etc/postfix/master.cf

A service that isn't running (e.g., Amavis, SpamAssassin, or Dovecot). Syntax errors in master.cf . 3. Common Solutions A. Dovecot LMTP Permissions If your config mentions a transport like private/filter

unix_listener /var/spool/postfix/private/auth mode = 0660 user = postfix group = postfix Use code with caution. B. Service Crashes

Before changing any configuration files, pinpoint the exact domain or email triggering the error. Use grep to pull the specific log entries from your mail log file (usually located at /var/log/mail.log or /var/log/maillog ). sudo grep "unknown mail transport error" /var/log/mail.log Use code with caution.

This is the most common cause. If you recently edited /etc/postfix/master.cf to add a content filter (like Amavis, Rspamd) or a custom delivery agent, a syntax typo will crash that specific transport daemon. Common Solutions A

Verify that the server has enough free space and memory.

Ensure the queue directories are owned by the postfix user:

Example:

Are you using a (like Amavis or Rspamd)? Is this happening for all domains or just one? What Linux distribution are you running? Share public link

Seeing "delivery temporarily suspended: unknown mail transport error" in your Postfix mail logs ( /var/log/mail.log or via journalctl ) means your mail server has completely stopped trying to deliver emails to a specific destination. This is a generic, catch-all error. It triggers when the Postfix queue manager encounters an unexpected failure from a delivery agent (like smtp , local , virtual , or dovecot ) and cannot safely determine the root cause.