If you are not able to login Horde and you are getting an Error that “Your Internet Address has changed since the beginning of your Mail session. To protect your security, you must login again.” follow the below steps to fix this error:-
1) First login to Horde and then turn off the ‘checkip’ feature.
2) Through root SSH login to Plesk control panel and edit the /usr/share/psa-horde/config/conf.php file in your text editor. Also Change the below lines:
$conf['auth']['checkip'] = true;
$conf['auth']['checkip'] = false;