How MailHurdle Protects You from Spam E-Mail

MailHurdle basically works this way:  

1. When the W & M E-Mail Server receives E-Mail addressed to you it checks its sender address against a list of addresses who have already sent you E-mail; if it sees the sender on the list, you get the message.
2. Otherwise if the E-Mail server sends a message to the sending equipment, telling it that W & M’s server is busy, resend later. If the sender is a typical E-Mail server it resends and this message gets to you; then the address of the sender gets put on the list; any E-Mail with that address reaches you thereafter.
3. If the sender is just squirting out spam mail to a slew of addresses, the sender does not resend; thus the spam will not reach you.
4. There are occasions when the sending server is not sophisticated enough to resend in responds to the testing “try again” message from MailHurdle; then the legitimate message is barred from reaching you. Even then the sender will receive a message that their message did not go through; in most cases the sender typically resends (but not the Spam sender). The resent mail goes through; and thereafter because it goes on the acceptable list.

 http://www.wm.edu/it/mailhurdle