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Iowa State University implemented greylisting back in 2004 and the results were immediate and dramatic. While it was true there were some broken MTA's back then that dropped the message instead of retrying, so many sites have implemented greylisting now they are few and far between. ISU does provide an opt-out option for users that do not wish to be greylisted. Honestly I was surprised MSU wasn't greylisting already! Joe -----Original Message----- From: MSU Network Administrators Group [mailto:[log in to unmask]] On Behalf Of Russell J. Lahti Sent: Friday, March 02, 2007 11:31 PM To: [log in to unmask] Subject: Re: [MSUNAG] New spam-fighting technique for mail.msu.edu going to DDC mailing list I can't tell you how many broken MTA's there are out there that will not handle a TEMPFAIL correctly, and junk the mail instead of queuing it for later delivery attempts. While I definitely don't have much sympathy for the people running these non-RFC compliant systems, they definitely are out there, and answering the question of: Will greylisting block valid email messages? With the response: No. Greylisting will eventually allow all valid mail servers that resend messages to mail.msu.edu to process normally. is a slight bit misleading. There is a definite chance that what an end user might consider legitimate mail might be lost by implementing greylisting. While a vast majority will work normally, some will likely not. For example, web apps that have been developed to emulate an SMTP conversation instead of dumping the mail to an MTA queue for delivery, etc. I'd be interested in what others have run across in their greylisting endeavors. The few times that I have seen it implemented I have also seen it removed. -Russell > -----Original Message----- > From: MSU Network Administrators Group > [mailto:[log in to unmask]] On Behalf Of Edward R Kryda > Sent: Friday, March 02, 2007 2:14 PM > To: [log in to unmask] > Subject: [MSUNAG] New spam-fighting technique for > mail.msu.edu going to DDC mailing list > > NAG has asked that we give a heads-up when we send mailings > related to computing at MSU to MSU's Deans, Directors, and > Chairs (DDC) list. > The following mailing from Tom Davis, director of ACNS, will > go to DDC soon. > > Edward Kryda > Email Team Leader > mail.msu.edu > > ============================================================== > ========= > To: Deans, Directors, and Chairs > Subject: New spam-fighting technique for mail.msu.edu > > Unsolicited commercial e-mail, or spam, annoys us all and > inhibits our productivity. Industry experts estimate that at > least 80% of all Internet e-mail is now spam. Mail.msu.edu > processes up to four million messages per day, blocking about > half as spam. > > To combat this problem, the ACNS mail team will add a new > feature to mail.msu.edu on March 7, a technique called > "greylisting." Rather than attempting to identify spam based > on the content of the message, greylisting blocks spam based > on the behavior of the remote e-mail server. > > When first installed, greylisting will introduce a temporary > delay in the receipt of incoming e-mail (as it "learns" which > remote e-mail servers can be trusted). Delays will be as > little as 5 minutes to as much as a few hours, depending on > the configuration of the sender's e-mail server. These > delays will fade within a day or so. > > Greylisting is another tool to fight the scourge of spam. Our > existing spam techniques have strained our mail servers and > introduced e-mail delays due to the sheer volume of messages > being processed. We expect the implementation of greylisting > to improve this situation. > > The ACNS mail team will carefully monitor the performance of > this new procedure. If you note any problems or have > questions, contact the ACNS Help Desk at (517) 432-6200. For > more information, please visit: > http://techbase.msu.edu/viewpathfinder.asp?id=7772&service=help > > Tom Davis, Director > Academic Computing and Network Services >