Greylisting is the name of a method that is used to reduce the delivery of junk e-mail but allow legitimate e-mail messages to be delivered.
Greylisting looks at the IP address of the sender and the recipient address. If the system does not recognize this information, then it will temporarily reject the e-mail. All legitimate e-mail systems will attempt to resend the e-mail at a later time, and the e-mail will go through.
Most applications that send junk e-mail just send junk e-mail messages once and do not attempt to resend them. These junk e-mail applications use the "fire-and-forget" method, which means that if the junk e-mailer was unsuccessful at sending junk e-mail to a particular e-mail address, the application will not try to resend that e-mail message.
Greylisting does not delete legitimate e-mail messages. All legitimate e-mails will go through using greylisting. The only potential effect greylisting may have for AISO.Net customers is a slight delay in the delivery of legitimate e-mail messages.
However, these delays can be avoided by adding e-mail addresses to yourÂ "Whitelist" list. Any e-mail address in your "Whitelist" list will not be subjected to greylisting. In addition, if you do experience a delay with a certain e-mail address, you usually will not experience that delay again over the next 30-day period.
For more information on greylisting click here: http://www.aiso.net/spam-protection.asp