Not able to log in to Webmail/IMAP on Plesk for Linux server: error: Permission denied

Symptoms

• Unable to log in to Webmail/IMAP for example.com. It fails with the below errors:

  CONFIG_TEXT: courier-imapd: info@example.com: chdir(/var/qmail/mailnames/example.com/info) failed!!
  courier-imapd: error: Permission denied
  courier-imapd: LOGIN FAILED, method=PLAIN, ip=[::1]
  courier-imapd: authentication error: Permission denied

  or

  CONFIG_TEXT: dovecot: service=imap, user=info@example.com, ip=[127.0.0.1]. Error: opendir(/var/qmail/mailnames/example.com/applications/Maildir) failed: Permission denied (euid=30(popuser) egid=31(popuser) missing +r perm: /var/qmail/mailnames/example.com/applications/Maildir, we're not in group 516)

Cause

Incorrect permissions for the /var/qmail/mailnames/example.com/ directory.


Resolution

1. First of all, make sure that the error is the same as in the title.
2. After that, log into the server via SSH.
3. Try to repair permissions automatically:

   # plesk repair mail example.com

4. In case it will not help, make sure that permissions to /var/qmail/mailnames/example.com/ and all the directories and files inside are similar to the one shown below:

   # stat /var/qmail/mailnames/example.com/ | grep Access
   Access: (0750/drwxr-x---) Uid: ( 30/ popuser) Gid: ( 31/ popuser)
   Access: 2015-12-23 16:59:20.527983735 +0700