New features in recent releases of e-Mail notify include the ability to launch an external mail client, the ability to monitor multiple mailbox accounts, options for Quick Viewing and Quick Deletion of mail, and dial-up network control (e-Mail Notify automatically dials your internet provider, retrieves your mail headers, and then hangs up).
Like Post Office, e-Mail Notify only checks for mail (it's not a reader); however, it can also easily launch the mail client of your choice when mail arrives. The advantage to using e-Mail Notify over a regular mail client for checking mail is that it takes up a minimum 2-3% of system resources, as opposed to a normal mailreader, which can suck up anywhere from 7-10% of your system's resources.