dovecot out of memory due to vsz_limit

Symptoms

Roundcube gives internal server errors, the LMTP service is down, or messages similar to the following appear in /var/log/maillog.

CONFIG_TEXT: Jun  1 13:16:18 server dovecot: lmtp(user@domain.tld)<458640><kWHRLJIbeGSQ/wYAoeKyhw>: Fatal: master: service(lmtp): child 458640 returned error 83 (Out of memory (service lmtp { vsz_limit=512 MB }, you may need to increase it) - set CORE_OUTOFMEM=1 environment to get core dump)

Cause

Mailboxes with a large number of messages can cause the LMTP server to consume all its allocated memory, resulting in the service crashing. To correct this, the vsz_limit  value for the LMTP configuration needs to be increased.

Resolution

1. Log in to WHM as the root user.
2. Navigate to Home / Service Configuration / Mailserver Configuration.
3. Scroll down to the Process Memory Limit for Mail (MB) option.
4. Set the option to the desired value.
5. Scroll down to the bottom of the page.
6. Click the Save Changes button.

Additional Resources

Mailserver Configuration