Warnings in /var/log/maillog on Plesk server: client_limit is lower than required under max. load

Symptoms

• These warnings can be seen in /var/log/maillogor /var/log/messages:

  CONFIG_TEXT: dovecot: config: Warning: service auth { client_limit=1000 } is lower than required under max. load (1396)
  dovecot: config: Warning: service anvil { client_limit=1000 } is lower than required under max. load (1399)

• Roundcube shows 500 Internal Server Error with the following errors in /var/log/httpd/error_log file:

  CONFIG_TEXT: [fcgid:warn] [pid 12406:tid 140260554016512] [client 203.0.113.2:42198] mod_fcgid: read data timeout in 45 seconds, referer: http://webmail.example.com/
  [core:error] [pid 12406:tid 140260554016512] [client 203.0.113.2:42198] End of script output before headers: index.php, referer: http://webmail.example.com/

• Mail clients might fail to connect.

Cause

The default_client_limit parameter is too low for Dovecot.

Resolution

1. Connect to the server via SSH

   Note: If direct SSH access to the server is not possible, contact server administrator for further assistance.

2. Create /etc/dovecot/conf.d/10-master.conf file using text editor to change client_limit for all dovecot services:

   CONFIG_TEXT: default_client_limit = 1500

3. Restart dovecot to apply the changes:
   

   # service dovecot restart

Note: If after raising the default_client_limit the same error message still showing up, increase more the limit.