What are identities ?
Identities are the sender addresses of your e-mail. When you send e-mail, you can choose between different identities and thus between your actual address and your mail alias as sender. This sender address then appears in the recipient's From field. Make sure that your sender is a working address, otherwise you will not be able to receive a reply.
How do I set up an identity ?
To create or edit an identity, navigate in the Webmailer (Horde) via `gearwheel´ -> `User settings´ -> `Webmail´ to your mail settings. In the column `Your details´, select the entry `Personal details´. Now you can define an identity in the drop-down menu and edit the information about it afterwards.