I know a lot of readers know already what push e-mail is. Wait -- I don't have a lot of readers here. :-) But anyway, I was trying to make a post about push e-mail but realized that some would actually ask what push e-mail is. So, let me try to put it in as simple terms as possible.
If you checked Wikipedia, it would say:
Push e-mail is used to describe e-mail systems that provide an always-on capability, in which new e-mail is actively transferred (pushed) as it arrives by the mail delivery agent (MDA) (commonly called mail server) to the mail user agent (MUA), also called the e-mail client. E-mail clients include smartphones and, less strictly, IMAP personal computer mail applications.
First, the concept of "pull" e-mail
To understand it better, it would probably be better to compare it with the traditional or conventional e-mail setup where the orientation is "pull" instead of "push". You see, when an e-mail is sent to your address/account, it will be stored first in a server (either in your ISP's server or in a web-server if the e-mail is server based). For example, if you have a Gmail account, any new e-mail sent to you will be stored first in Google's servers. It will remain there until you actually login to your email account, after which, your e-mail client (Gmail) will fetch that new e-mail from the Google's servers and will be made available to you (almost instantaneously) for you to read. What you did is that you logged in to Gmail to "pull" any new e-messages sent to you.
And now, push versus pull
Push email has the capability to "push" new messages from where it came from directly to its client as soon as it arrives. This does not require you to login to your client anymore and collect or "pull" your message. It's almost the same as a text message or SMS -- you receive them through your client (or in this case, your smart phone0 as soon as they are sent. Again, you don't need to login to your client to pull any new messages -- new messages are pushed to you. There. :-)
I think the most successful device which was able to utilize this is Research In Motion's (RIM) Blackberry. If you have a Blackberry, chances are, you are availing of its push e-mail technology.
Alright, next time, I can write my push e-mail post. Plus Nokia. Plus Smart Telecommunications. And of course, plus Google Apps.