Dovecot fails to start on Plesk server: Address family not supported by protocol

Symptoms

• Dovecot fails to start with the following error:

  # /etc/init.d/dovecot start
  Starting Dovecot Imap: Error: socket() failed: Address family not supported by protocol
  Error: service(managesieve-login): listen(::, 4190) failed: Address family not supported by protocol
  Error: socket() failed: Address family not supported by protocol
  Error: service(pop3-login): listen(::, 110) failed: Address family not supported by protocol
  Error: socket() failed: Address family not supported by protocol
  Error: service(pop3-login): listen(::, 995) failed: Address family not supported by protocol
  Error: socket() failed: Address family not supported by protocol
  Error: service(imap-login): listen(::, 143) failed: Address family not supported by protocol
  Error: socket() failed: Address family not supported by protocol
  Error: service(imap-login): listen(::, 993) failed: Address family not supported by protocol
  Fatal: Failed to start listeners
  [FAILED]

• Cannot add Service node to Plesk Multi Server with the following error:

  ERR [extension/plesk-multi-server] Task run failed with message 'Failed API request: [2019-06-27 04:00:16] DEBUG [util_exec] [cddf211e6612a5fb6a2995d4b33a4634-0] Starting: mailmng-imap --set-connections-limit --limit=1024
   [2019-06-27 04:00:17] DEBUG [util_exec] [cddf211e6612a5fb6a2995d4b33a4634-0] Finished in 0.69491s, Error code: 1
   [2019-06-27 04:00:17] ERR [util_exec] proc_close() failed ['/usr/local/psa/admin/bin/mailmng-imap' '--set-connections-limit' '--limit=1024'] with exit code [1]
   Unable to update the maximum number of connections: 'mailmng-imap failed: ''

Cause

Dovecot is configured to listen to IPv4 and IPv6 interfaces by default, but there are no IPv6 interfaces on the server.

Resolution

1. Connect to the server via SSH

2. Create new file in the /etc/dovecot/conf.d/:

   # touch /etc/dovecot/conf.d/25-custom-stats.conf

   Note: Prefixes 10 through 20 and 90 through 95 (inclusive) are reserved for Plesk. Please do not occupy them or edit files with these prefixes!

3. Add the following content to the file:

   # Dovecot custom setting for listening IPv4 only
   listen = *