We found this issue to be associated usually with users forwarding email to a Yahoo account. If spam slips by our spam filters and gets forwarded where the enduser reports it as spam not realizing the impact on their actions. In the last couple of years we have been not allowing people to forward their accounts to yahoo, aol, hotmail, etc. Too much of a headache. Chuck -----Original Message----- From: Micheal Patterson [mailto:micheal@spmedicalgroup.com] Sent: Tuesday, February 24, 2009 7:28 PM To: nanog@nanog.org Subject: Yahoo and their mail filters.. This may be old news, but I've not been in the list for quite some time. At any rate, is anyone else having issues with Yahoo blocking / deferring legitimate emails? My situation is that I host our corporate mx'ers on my network, one of the companies that we recently purchased has Yahoo hosting their domains mail. Mail traffic to them is getting temporarily deferred with the "421 4.7.0 [TS01] Messages from xxx.xxx.xxx.xxx temporarily deferred due to user complaints - 4.16.55.1; see http://postmaster.yahoo.com/421-ts01.html" The admin of the facility has contacted Yahoo about this but their response was for "more information" when they were told that traffic from my mx to their domain was to being deferred. I may end up just having them migrate to my systems just to maintain company communications if we can't clear this up in a timely manner. -- Micheal Patterson