Unable to log in to Webmail inside of cPanel (Horde, Roundcube, Squirrelmail)
If you are unable to log in to any of the webmail clients, start by checking the secure log.
If you see something like the following:
dovecot-wrap error changing uids: error: 1 (Operation not permitted)
This means that the dovecot-wrap program has the wrong permissions set. To resolve this, you will need to set the suid permission on that program. You can do this by issuing the following command:
chmod 4750 /usr/local/cpanel/bin/dovecot-wrap
This will set the correct permissions and resolve the issue.