On Mon, 27 Dec 2010 12:37:00 -0800 Ted Mittelstaedt <t...@ipinc.net> wrote:
> greylisting, though, is by far the best. But I have noticed an > increasing number of sites out there - and this is large sites - who > apparently are honked-off that people greylist, and they will bounce > delivery of mail that is issued an error 4xx in violation of the > standard. Off the top of my head I seem to remember seeing this from > several airline company mailers that send out the advertisements to > their frequent flyer members, and that send out electronic ticketing > receipts. Jerks! What you may be seeing is marginal SMTP client software that doesn't know how to handle a 4xx response to RCPT. There was even some commercial software that couldn't deal with this properly (Novell Groupwise, I believe, though it has long since been fixed in that product.) BTW, this is another reason we do our greylisting post-DATA. Although it's slower and uses more bandwidth, it does avoid problems with marginal SMTP clients and it does let us use the Subject: as part of the greylisting tuple, which greatly increases greylisting effectiveness. We do not find virus-scanning before spam-scanning to be effective. A tiny percentage of our mail is flagged as containing a virus, so it doesn't really reduce the amount of mail that would need to be spam-scanned. Regards, David.
