Here are some abbreviations that can be used in association with email.

advTHANKSance a cute way saying Thanks In Advance.

BTW Abbreviation for By The Way.

CRM Abbreviation for Customer Relationship Management.

EOM Abbreviaton for End of Message.

FWTW Abbreviation for For What It's Worth.

FYI Abbreviation for For Your Information.

GMTA Abbreviation for Great Minds Think Alike.

IHAC Abbreviation for I Have A Customer.

IMHO Abbreviation for In My Humble Opinion or In My Honest Opinion.

IMNSHO Abbreviation for In My Not-So-Humble Opinion.

NRN Abbreviation for No Reply Needed.

OT Common abbreviation for Off-Topic.

OTOH Abbreviation for On The Other Hand.

RFC Abbreviation for Request For Comments.

ROTFL Abbreviation for Rolling On The Floor Laughing.

ROTFLMAO Abbreviation for Rolling On The Floor Laughing hard.

RSN Abbreviation for Real Soon Now. It is usually used jokingly when something has been promised (and delayed) for a long time. If you see this, you can probably assume that it won't be ready anytime soon.

RTFM Abbreviation for Read The Manual.

TIA Abbreviation for Thanks In Advance.

UCE Abbreviation for Unsolicited Commerical Email.

YMMV Abbreviation for Your Mileage May Vary, this is a standard disclaimer used in vehicle ads in the U.S. It means that the author realizes that the readers' experience may be different than this.