Originally an ASCII text-only communications medium, Internet email was extended by Multipurpose Internet Mail Extensions (MIME) to carry text in other character sets and multi-media content attachments.
Commonly used wherever people get online -- including IMing, SMSing, cell phones, Blackberries, PDAs, Web sites, games, newsgroup postings, in chat rooms, on blogs, or on social media -- these abbreviations are used by people around the world to communicate with each other.
Net Lingo is also tracking a global list of worldwide text terms and international online jargon!
Acronyms have always been an integral part of computer culture, and they have since spawned a new language on the Internet.
Some early email systems required the author and the recipient to both be online at the same time, in common with instant messaging.
Today's email systems are based on a store-and-forward model.
Email servers accept, forward, deliver, and store messages.
Neither the users nor their computers are required to be online simultaneously; they need connect only briefly, typically to a mail server, for as long as it takes to send or receive messages.
Commonly thought of as a series of letters that make up a 'word' there is a distinction between acronyms and shorthand.
The actual definition of an acronym and text shorthand is here.