Roundcube, POP3, IMAP unable to connect (out of memory)

If you’re unable to connect to Roundcube, POP3, or IMAP, first verify that Dovecot is running:

systemctl status dovecot

If Dovecot is active but connections still fail, check the logs for out-of-memory errors like:

imap-login: Fatal: Failed to read config: mmap(/var/run/dovecot/config) failed: Cannot allocate memory
pop3-login: Fatal: Out of memory (service pop3-login { vsz_limit=128 MB }, you may need to increase it)
managesieve-login: Fatal: Out of memory (service managesieve-login { vsz_limit=128 MB }, you may need to increase it)

These errors indicate the default 128 MB memory limit for Dovecot login processes is too low.

Solution

Increase the Process Memory Limit for Authentication to 256 MB using one of these methods:

• Via WHM: Navigate to Mailserver Configuration and increase the Process Memory Limit for Authentication (MB) to 256.
• Via command line: Edit /var/cpanel/conf/dovecot/main and change login_process_size from 128 to 256.

Restart Dovecot after making the change:

systemctl restart dovecot