Intermittent mail connectivity issues due to the process limit being reached

Symptoms

Users intermittently encounter login failures, 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.

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

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

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

Description

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 settings, may need to be increased on servers with a high number of users connecting simultaneously.

Workaround

1. Login 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.
   Please note that increasing the setting too much can cause server instability. The value should be increased in increments of 5 or 10 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