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Email - Greylisting FAQ
This article answers some frequently asked questions about Greylisting, a spam filtering technique.
Greylisting can significantly reduce junk mail by requiring unfamiliar email servers to re-send a message before accepting it for delivery. Most automated spam servers will not re-send on request, thus eliminating many unwanted messages. However, servers that comply with email standards will re-send their messages, allowing them to pass through the barrier and arrive in your email box.
You will only get one copy of a message, which you'll receive after the email service re-sends the message.
Eventually, spammers will come up with a way around greylisting--and yes, sending everything twice is one such way (though it's a bit more complicated than that at the technical level). At present time, however, most spammers do not adhere to Internet standards when sending their email and greylisting will work as long as that is the case.
No. Email servers that comply with email standards will re-send their messages without the sender having to do anything.
It depends on the type of junk mail that you receive. It will eliminate spam from email servers that do not conform to Internet standards.
The first time a given remote email server tries to send an email message to an @uchicago address, email will be delayed until the remote server re-sends that message. (Typically, this will be 5-20 minutes, but it depends on the configuration of the remote server.) Once the remote server re-sends the message and is added to the approved list, email from that server will flow normally again.
No. This only affects email sent from email servers outside the University with which we have not had previous contact.
Greylisting blocks all messages that do not comply with email standards. If someone sends you a "valid" email message from an email server that does not comply with email standards, greylisting will block it.
No. Greylisting works in conjunction with the Junkmail service. Greylisting is just an additional way we are blocking spam from University email accounts.
No. Messages that are not re-sent don't come in contact with our servers, and therefore are not added to your quarantine.
No. Greylisting is set up for the entire central email system.