Roundcube webmail is not accessible after an upgrade to Plesk Onyx 17.8 on Centos 6

Symptoms

• Roundcube webmail is not accessible after an upgrade to Plesk Onyx 17.8 on CentOS 6. The following error message is shown in a browser:

  PLESK_INFO: Internal Server Error
  The server encountered an internal error or misconfiguration and was unable to complete your request.
  Please contact the server administrator, root@localhost and inform them of the time the error occurred, and anything you might have done that may have caused the error.
  More information about this error may be available in the server error log.

• The following message appears in the logfile /var/log/plesk-roundcube/errors:

  CONFIG_TEXT: IMAP Error: Login failed for user@example.com from 203.0.113.2(X-Real-IP: 203.0.113.2,X-Forwarded-For: 203.0.113.2). Empty startup greeting (localhost:993) in /usr/share/psa-roundcube/program/lib/Roundcube/rcube_imap.php on line 196 (POST /roundcube/?_task=login&_action=login)

• The Roundcube version is 1.3:

  # rpm -qa | grep round
  plesk-roundcube-1.3.4-cos7.build1708180228.17.noarch

• The system PHP version is 5.3:

  # php -v
  PHP 5.3.3 (cli) (built: Mar 22 2017 12:27:09)

• Horde webmail works fine.

Cause

According to Rouncube requipments, Roundcube version 1.3 requires PHP version 5.4 or greater.

Resolution

Upgrade the system PHP to version 5.4, for example from Atomic repository:

1. Connect to the server via SSH.
2. Install atomic repository by executing this command:
   

   # wget -q -O - https://atomicorp.com/installers/atomic | sh

3. Run PHP upgrade:

   # yum install php

Note: PHP upgrade is non-Plesk related and should be done by server's administrator.

Alternatively, switch to Horde or change the PHP version for Roundcube webmail according to the KB article:

• How to change a PHP version for webmail on Plesk for Linux