The easiest way to get in touch with either the staff in general or a specific Immortal is through the Forums. Many Immortals have a forum dedicated to the discussion of their religion or cabal. Likewise, most Immortals can be reached at their name at carrionfields dot com.
If you specifically wish to contact an Administrator, please read HELP ADMIN.
Lastly, you can always send a note to "IMMORTAL" in-game to address the Immortal staff.