Cannot log in into Rouncube on some domains: Connection to storage server failed

Symptoms

• Cannot log in into Roundcube on some domains:

  PLESK_ERROR: Connection to storage server failed

  ---

  PLESK_ERROR: Server Error: SELECT: Internal error occurred. Refer to server log for more information.

  ---

  The following error is shown upon log in to Roundcube:

  CONFIG_TEXT: An error has occurred !
  Server error: STATUS: Internal error occurred. Refer to server log for more information. [2018-11-15 16:15:30] (0.001 + 0.000 secs).

• The error like the following can be found in /var/log/maillog:

  CONFIG_TEXT: # cannot chdir to domain dir example.com: Permission denied

  ---

  CONFIG_TEXT: courier-imaps: john.doe@example.com: Account's mailbox directory is not owned by the correct uid or gid

  ---

  CONFIG_TEXT: dovecot: Error: service=imap, user=john.doe@example.com, ip=[83.157.102.43]. Mailbox INBOX.Spam: open(/var/qmail/mailnames/example.com/john.doe/Maildir/.Spam/dovecot-uidlist) failed: Permission denied

• Permissions for the folder /var/qmail/mailnames/example.com or /var/qmail/Mailnames/example.com/john.doe differ from the following:

  # ls -ls /var/qmail/mailnames | grep example.com
  4 drwx------ 5 popuser popuser 4096 example.com
  
  # ls -la /var/qmail/mailnames/example.com/john.doe
  drwx------ 6 popuser popuser 4096 Maildir

Cause

Wrong permissions for /var/qmail/Mailnames/example.com folder or /var/qmail/Mailnames/example.com/john.doe.

Resolution

1. Connect to the server via SSH.

2. Run the following command to fix the ownership for mailfolders:

   # chown -R popuser:popuser /var/qmail/mailnames