The easiest way to get in touch with either the staff in general or a specific Immortal is through the Forums.
You may email all of the Immortals at imms@carrionfields.com or only the Implementors (level 60) at imps@carrionfields.com.
Also, every active Immortal (usually those who appear under the 'wizlist' command) can be reached at their Immortal name at carrionfields.com (e.g., scarabaeus@carrionfields.com).
Lastly, you can always send a note to "IMMORTAL" in-game to address the Immortal staff.