dovecot.index.cache: Cannot allocate memory

Symptoms

A user is unable to load their inbox in Roundcube and messages similar to the following may be found in /var/log/maillog:

CONFIG_TEXT: Apr 24 20:08:50 server dovecot[3670167]: imap(user@domain.tld)<3693787><A3EA5hj6XJd/AAAB>: Error: Mailbox INBOX: mmap(size=433701832) failed with file /home/cpuser/mail/domain.tld/user/dovecot.index.cache: Cannot allocate memory

Cause

This issue occurs when the Dovecot index file is larger than Dovecot's Process Memory Limit. Increasing this limit will allow the inbox to load.

Resolution

1. Log in to WHM as root
2. Navigate to Home / Service Configuration / Mailserver Configuration

3. In the Process Memory Limit for Mail (MB) textbox, enter a value greater than the mmap size seen in the maillog error

   Note: The mmap size is in bytes

4. Click the Save Changes button at the bottom of the page