Push and Pull e-mail
The traditional method of receiving electronic mail (e-mail) used pull technology (such as POP). In this scenario you configure your e-mail to periodically connect to your e-mail provider and retrieve any message.
In a mobile environment where data rates are still chargeable this can be problematic as polling every fifteen minutes (or more frequently) can quickly build up your data charges.
In a push e-mail environment an initial connection is made from your client to the e-mail server and the connection between the two is kept open for periods of time. Some systems use a regular pulse-signal (also called a ping and a heartbeat) to tell the connection to stay alive (this is a much smaller overhead than performing a full poll).
I was surprised recently to hear someone tell me that Blackberry is the only push e-mail provider - maybe this was true a long time ago but these days Microsoft ActiveSync is a competitive push e-mail technology.
This definition has been bought to you by: Jason Slater Weblog Tech Fact.