Push email differs from conventional email systems that are “pull” oriented. Usually, when email is sent, it arrives at the recipient’s Internet Service Provider’s (ISP’s) mail server, where it is held for collection. It might instead arrive at a website server, if the email is Web-based. Either way, email remains on the mail server until the recipient uses an email program to poll the mail server. If new mail is present, the email client “pulls” the mail to the client’s computer. The difference between this scheme and push email is that, with push email, the mail is pushed through to the client without waiting for polling.
For BES and BIS, the blackberry servers monitors these e-mail servers, and when it sees new e-mail for the user, it retrieves (pulls) a copy and then pushes it to the BlackBerry handheld device over the wireless network, something much like an sms.