Re: [44net] hotmail

Greylisting works by refusing incoming mail with a code 421 the first time it's offered by the sending IP address, forcing the sender to retry the delivery at least a minute later. (421 means "temporary failure, too busy, try again later"). This works against a lot of spam because generally, most spammers are "hit and run"; they don't retry. Hotmail was doing the right thing there, retrying a few minutes later, but the retry was coming from a different IP address each time, so it never managed to establish that it was a retry and get past the greylister. A more sophisticated greylister might have noticed that the hostname retrying was coming from the same domain (*.protection.outlook.com), but the greylister we have only works with IP addresses, not domains. I solved the inbound problem, at least in the short term, by getting a list of all the IP addresses used by hotmail and its cousins, and adding those addresses to the greylister's "whitelist", thus allowing the mail in on the first try. This list is available from Microsoft as a 'technet' article: https://technet.microsoft.com/en-us/library/dn163583(v=exchg.150).aspx This will work until they add more addresses, but they claim that changes to the list are rare. There are thousands of addresses in the list so maybe they have enough and it'll remain static for a while. (We didn't used to have this problem because the mailing list host was 'hamradio.ucsd.edu' and was behind UCSD's spam filters, which use a different mechanism. But 'hamradio' is being shut down so the list had to move to a different provider. So the inbound problem is solved for now. Outbound mail disappearing inside hotmail remains a problem. Some hotmail people seem to be getting the mailing list mail, others not. I've asked one (Ronen) who has not been getting the mailing list mail to check his spam settings carefully, and make sure that the mail isn't being routed to his 'junk' mailbox. But there may be nothing we can do about it except to have him change email services. I'm not sure gmail will be better, but so far it's been less of a bother. - Brian