Unable to read mail in Horde or Roundcube on Plesk for Linux: Cannot allocate memory due to vsz_limit

Symptoms

• Plesk Obsidian running on a Linux-based operating system

• Unable to read mail in the Horde or Roundcube webmail clients:

  CONFIG_TEXT: IMAP error reported by server

  CONFIG_TEXT: INTERNAL ERROR
  Could not load message from server

• 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

• Running the systemctl status dovecot command shows output that is similar to the following:
  

  CONFIG_TEXT: Apr 08 18:08:06 server dovecot[3588064]: master: Error: service(config): command startup failed, throttling for 60.000 secs
  Apr 08 18:08:06 server dovecot[3588173]: config: Fatal: master: service(config): child 3868141 returned error 83 (Out of memory (service config { vsz_limit=256 MB }, you may need to increase it) - set CORE_OUTOFMEM=1 environment to get core dump)

Cause

The maximum limit for Dovecot process address space (vsz_limit) has been 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. Log into the Plesk server via SSH

2. Open (or create) the file /etc/dovecot/conf.d/99-vsz.conf with your favorite command-line text editor and Increase vsz_limit value in the dovecot configuration by adjusting the contents as follows:
   

   CONFIG_TEXT: service imap {
   vsz_limit = 1 G
   }
   
   default_vsz_limit = 1 G

3. Reload the Dovecot service in order to apply the changes:

   # systemctl reload dovecot