Quoting Steven Champeon (schampeo@hesketh.com):
It's not really my business why a hotmail.com MX accepted mail it couldn't deliver. I could care less /why/. It's up to hotmail to fix their systems - I don't care how they perform that background check on quota.
Exactly.
It's my business that over the past sixty days, we've had to reject over 23K of these, and had rejected some 130K in three weeks during March, at the peak of the joe job. At one point, backscatter accounted for 70% of my inbound email traffic on one host. Almost made the usual spam and virus look like background noise.
36K backscatter rejects from hotmail yesterday but only 2K from AOL. AOL has really got their act together compared to hotmail, verizon, comcast, and the like. May 18 00:00:05 mx1 postfix/smtpd[11977]: 6F8F315DC0: reject: RCPT from mc1-s21.bay6.hotmail.com[65.54.163.161]: 550 <xjlljuzisexmj@tuffmail.co.uk>: Recipient address rejected: User unknown; Probably forged by Alan Ralsky; from=<> to=<xjlljuzisexmj@tuffmail.co.uk> proto=ESMTP helo=<mc1-s21.hotmail.com> It was 80K daily from hotmail till I dropped the MX records for 4 of the domains being forged. If anyone would like to test their capability to reject 1+ million a day I can point the MX records to your servers. :-) John Capo Tuffmail.com