Unable to log into RoundCube: Connection to storage server failed

Symptoms

1. Unable to log into RoundCube webmail:
   

   PLESK_INFO: Connection to storage server failed

   

2. The following errors could be found in /var/log/plesk-roundcube/errors:
   

   CONFIG_TEXT: [14-Aug-2017 12:30:59 -0700]: <mckf80c0> IMAP Error: Login failed for john.doe@example.com from 203.0.113.2(X-Real-IP: 203.0.113.2). Could not connect to localhost:143: Network is unreachable in /usr/share/psa-roundcube/program/lib/Roundcube/rcube_imap.php on line 193 (POST /roundcube/?_task=login&_action=login)

3. Nothing is listening on port 143:
   

   # netstat -tunap | grep 143
   #

Cause

Dovecot service is down.

Resolution

1. Connect to the server via SSH;

2. Check the Dovecot service and start it:

   # systemctl status dovecot.service
   ● dovecot.service - Dovecot IMAP/POP3 email server
   Loaded: loaded (/lib/systemd/system/dovecot.service; disabled; vendor preset: enabled)
   Active: inactive (dead)

   # systemctl start dovecot.service