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.

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

Description

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.

Workaround

1. Log into WHM as the ‘root’ user.
2. Navigate to "Home / Service Configuration / Mailserver Configuration."
3. Scroll down to "Process Memory Limit for Mail (MB)."
4. In the "Process Memory Limit for Mail (MB)" textbox, enter a value greater than the mmap size seen in the maillog error.
   Please note that the mmap size is in bytes.
5. Scroll to the bottom of the page.
6. Click the "Save Changes" button.