On Jul 20, 2010, at 7:46 PM, Hector Santos wrote: > J.D. Falk wrote: > >> On Jul 20, 2010, at 8:09 AM, Hector Santos wrote: >>> It seem so random in what seems to be always accepting a transaction but >>> intermittently delivered or not. >> Are you talking about the 4xx replies? If you check the text of the reply, >> there's usually a URL with a bit more information about the reason. Same >> with 5xx, for that matter. > > I have not seen temporary rejects. All transactions accepted with 250. > However, it has been noted by others that YAHOO does employ greylisting (in > some form). But I have not seen the temporary negative reply codes.
It's not the wikipedia definition of greylisting, but they do use 4xx replies to control the flow of inbound mail. >> If you're saying the mail is just disappearing, it's possible that your >> users have configured their accounts to delete suspected spam instead of >> putting it in the spam folder. > > The issue is that its intermittent and not consistent. Send a test, with the > recipient on the phone, he gets it. Send another test, i.e, same message > with "TEST #2" as subject, it never arrives. Send "Test #3" it may or not > arrive, and so on. No pattern. I remember hearing some years ago that Hotmail's SVM filter had learned that an empty message with a subject of "test" was spam. They've probably fixed it since then, but it's a great example of how machine learning can lead to entirely logical but unexpected results. (I'm fairly certain Yahoo! Mail doesn't use any Microsoft software, though.) > However, at some point, we tried the reverse, yahoo to non-yahoo, which > arrived each time and then we try sending test messages again. For a moment > there, it appeared to work, so we presumed there was a YAHOO user based > "auto-white listing" to addresses the user sends mail to. I jumped on this > theory because we have that feature - local users can build an auto-white > list just by sending mail to to their "social/business" network. > > But then we try sending "test #4", "test #5" and so on and they done ever > arrive or go into any folder. > > Absolutely, no pattern, inconsistent "DISCARDING" and delivery of mail. Often, filters will be reacting to a system-wide pattern that an individual user can't see. To give an overly simplified and surely incorrect example, if a spammer were sending "test #4" all day, then your entirely legitimate "test #4" would get caught too. That said, if the mail is being discarded due to system-wide (rather than recipient-specific) filters, I'd personally prefer to see a 5xx reply instead. But: their system, their rules. > I really hope someone with the yahoo story can explain it. Like everyone else who writes anti-spam software, Yahoo! is not known for divulging their secrets. Though I did work there for a time, everything I've written here could be gleaned from public statements and general knowledge of the techniques a large mailbox provider is likely to employ. > I was somewhat watching to see/hear if there was a related to valid DKEY/DKIM > Brownie points or something now expected by YAHOO. But all I know so far > about that is that is required by BULK mail senders. We are not bulking > here. just individual single shot messages. DKIM isn't required to send mail, bulk or otherwise. Yahoo! does require DKIM for non-ISPs to subscribe to their complaint feedback loop, but doesn't automatically provide any brownie points. Single shot messages are always the hardest to diagnose, since you can't see a pattern -- and if you send enough to create a statistically significant pattern, the spam filters will notice it too.
