Hello Andrea,
Thank You for your kind words of appreciation and feedback about our service.
I have checked and found that your account is hosted on one of our shared server SWINDON.
We have MailEnable Enterprise Edition with MEwebmail support on this server.
MEwebmail web interface can be accessed at :-
http://serverIP/MEwebmail
It will redirect you to :-
http://serverIP/MEwebmail/HooDoo/lang/EN/login.aspx
serverIP = the same IP address that you use to access your Plesk panel.
Email account that you create in Plesk can be accessed using MEwebmail as well as Horde.
You have to use the same login details in MEwebmail which you are using while connecting with Horde.