An excellent resource for leaving Mormonism:
Email method for resignation (updated May 2011)
"Many people have reported that they have been able to resign via e-mail
directly to Membership Records. If so, this greatly simplifies the
resignation process. Your e-mail should include identifying information and a
mailing address for the confirmation letter. The following is a suggested form
(omit the bracketed material if you do not have it available):
To: "Greg Dodge, Membership Record"dodgegw@ldschurch.org>
Subject: Resignation of membership in LDS church
My full name is ______; my date of birth is ____________ . [I was baptized on
___(date). My membership number is ______.] My residence address is _______
[in the ________ ward/branch].
I hereby resign my membership in the Church of Jesus Christ of Latter-day
Saints, effective immediately, and request you to remove my name permanently
from your membership records. I wish no further contact from representatives
of your church except to confirm that my name has been removed from your
records. I expect to receive that confirmation within a reasonably short time.