Unable to read mail in Horde/Roundcube on Plesk for Linux: Cannot allocate memory

Symptoms

1. Unable to read mail in Horde/Roundcube:

   CONFIG_TEXT: IMAP error reported by server

   ---

   CONFIG_TEXT: INTERNAL ERROR
   Could not load message from server

2. The following errors appear in /var/log/maillog:

   CONFIG_TEXT: dovecot: service=imap, user=user@example.com, ip=[127.0.0.1]. Fatal: master: service(imap): child 688159 returned error 83 (Out of memory (service imap { vsz_limit=256 MB }, you may need to increase it) - set CORE_OUTOFMEM=1 environment to get core dump)

   ---

   CONFIG_TEXT: Error: mmap(size=0) failed with file /var/qmail/mailnames/example.com/user/Maildir/dovecot.index.cache: Cannot allocate memory

Cause

The maximum limit for Dovecot process address space was exceeded.

The size of the file /var/qmail/mailnames/example.com/user/Maildir/dovecot.index.cache is more than the default "vsz_limit" value:

# ls -alh /var/qmail/mailnames/example.com/user/Maildir/dovecot.index.cache
-rw------- 1 popuser popuser 500M Feb 27 11:21 /var/qmail/mailnames/example.com/user/Maildir/dovecot.index.cache

# doveconf | grep default_vsz_limit
default_vsz_limit = 256 M

Resolution

Note: if you don't have root access to Plesk via SSH, contact your hosting provider regarding the issue

1. Connect to Plesk server via SSH;

2. Open file in any text editor and Increase vsz_limit value in the dovecot configuration (if the file does not exist, create it and insert the content below):
   

   # vi /etc/dovecot/conf.d/99-vsz.conf
   service imap {
   vsz_limit = 1 G
   }
   
   default_vsz_limit = 1 G

3. Reload Dovecot:

   # systemctl reload dovecot.service