If the logs show a "Connection refused" or "No such file or directory" error for a socket, the software responsible for processing your mail has likely stopped running. Check the status of your security filters and delivery agents:
Postfix expects a service named dovecot to be explicitly defined in your master.cf file. If it is missing or misspelled, the unknown transport error occurs. Verify master.cf Service Definitions
To solve this, you must understand what the error components mean:
Maintain backups of master.cf and main.cf before making substantial changes. If the logs show a "Connection refused" or
Open your Postfix master configuration file.
: Postfix sub-daemons running inside an isolated jail ( chroot ) that cannot resolve core system network services. Step-by-Step Diagnostic & Resolution Workflow 1. Locate the Root Error in the Mail Log
What are the appearing right before the "delivery temporarily suspended" message? Share public link Verify master
After any manual edits to a main configuration file, always reload Postfix:
If permissions are resolved, force Postfix to immediately retry delivering the suspended messages: postfix flush Use code with caution.
: A transport name specified in main.cf (e.g., transport_maps , relayhost , or virtual_transport ) is missing its definition in master.cf . Step-by-Step Diagnostic & Resolution Workflow 1
: If you have manually defined a transport (e.g., filter ), ensure there is a corresponding entry at the beginning of a line in /etc/postfix/master.cf .
Mailbox directories or database sockets have incorrect ownership.
When Postfix processes an email, the qmgr (queue manager) hands the message off to a specific transport delivery agent (like smtp , local , virtual , or pipe ). If that delivery agent terminates abruptly or returns an invalid status code, qmgr panics, backs off, and labels the destination queue as temporarily suspended to protect system resources. The most common triggers include:
Open /etc/postfix/master.cf and ensure the service name matches exactly. For example, if main.cf specifies mailbox_transport = lmtp:unix:private/dovecot-lmtp , ensure that the dovecot-lmtp socket path is correct and Postfix has permission to read/write to it. 2. Permissions and Socket Ownership Issues
If the logs show a "Connection refused" or "No such file or directory" error for a socket, the software responsible for processing your mail has likely stopped running. Check the status of your security filters and delivery agents:
Postfix expects a service named dovecot to be explicitly defined in your master.cf file. If it is missing or misspelled, the unknown transport error occurs. Verify master.cf Service Definitions
To solve this, you must understand what the error components mean:
Maintain backups of master.cf and main.cf before making substantial changes.
Open your Postfix master configuration file.
: Postfix sub-daemons running inside an isolated jail ( chroot ) that cannot resolve core system network services. Step-by-Step Diagnostic & Resolution Workflow 1. Locate the Root Error in the Mail Log
What are the appearing right before the "delivery temporarily suspended" message? Share public link
After any manual edits to a main configuration file, always reload Postfix:
If permissions are resolved, force Postfix to immediately retry delivering the suspended messages: postfix flush Use code with caution.
: A transport name specified in main.cf (e.g., transport_maps , relayhost , or virtual_transport ) is missing its definition in master.cf .
: If you have manually defined a transport (e.g., filter ), ensure there is a corresponding entry at the beginning of a line in /etc/postfix/master.cf .
Mailbox directories or database sockets have incorrect ownership.
When Postfix processes an email, the qmgr (queue manager) hands the message off to a specific transport delivery agent (like smtp , local , virtual , or pipe ). If that delivery agent terminates abruptly or returns an invalid status code, qmgr panics, backs off, and labels the destination queue as temporarily suspended to protect system resources. The most common triggers include:
Open /etc/postfix/master.cf and ensure the service name matches exactly. For example, if main.cf specifies mailbox_transport = lmtp:unix:private/dovecot-lmtp , ensure that the dovecot-lmtp socket path is correct and Postfix has permission to read/write to it. 2. Permissions and Socket Ownership Issues
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