CMS Site Manager > Settings > Intranet & Collaboration:
General
Sender's e-mail
Senders e-mail address.
Sender's name
Name of the sender.
E-mail subject
Here you can add the subject of the event announcement message.
Help URL: http://devnet.kentico.com/docs/6_0/contexthelp/index.html?settings_intranetevents.htm