Intermittent mail connectivity issues due to the process limit being reached

Symptoms

Users intermittently encounter login failures, Dovecot restarts frequently, or cPanel sends notifications that IMAP has failed. 

Entries similar to one of the following can be found in the /var/log/maillog log file.

CONFIG_TEXT: Sep 16 15:50:42 servername dovecot: master: Warning: service(imap-login): process_limit (50) reached, client connections are being dropped

CONFIG_TEXT: Sep 16 11:41:57 servername dovecot: master: Warning: service(pop3): process_limit (64) reached, client connections are being dropped

CONFIG_TEXT: Sep 16 12:32:13 servername dovecot: master: Warning: service(imap): process_limit (512) reached, client connections are being dropped

Cause

Dovecot has several settings that limit the amount of system resources it consumes. The default values are sufficient for most servers. Some of these settings, such as the process_limit, may need to be increased on servers with a high number of users connecting simultaneously.

Resolution

1. Log in to WHM as the root user.
2. Navigate to Home / Service Configuration  / Mailserver Configuration.
3. Scroll down to the appropriate setting.
   • If the maillog entry contains service(pop3) or service(imap), locate the Maximum Number of Mail Processes setting.
   • If the maillog entry contains service(imap-login), locate the Maximum Number of Authentication Processes setting.

4. Increase the value as needed.

   Note: Over-increasing the setting can cause server instability. The value should be increased in small increments until the issue no longer occurs.

5. Scroll to the bottom of the page.
6. Click the Save Changes button.

Additional resources

Mailserver Configuration: Mailserver Configuration settings