For those using Plesk 9.x, Horde naively allows webmail logins via HTTP (in-secure) or HTTPS (secure). HTTP log-ins are not recommended as username and password information is sent in clear text across the Internet.
In the following example we’ll configure access to http://webmail.yourdomain.com to automatically re-direct to http://webmail.yourdomain.com.
NOTE: These instructions are specific to Plesk’s implementation of Horde but should work on any Horde 3.1.7 installation. Simply locate Horde’s “conf.php” file and adjust the parameters shown below.