Frank Bulk wrote:
Q> Does Yahoo! use "greylisting" to reject messages?
A> No. The most commonly understood form of "greylisting" is where an SMTP server will reject every message the first time it is attempted, and then accept it if the sending server retries later. The theory is that spammers won't retry messages, while legitimate senders will.
Yahoo! does not utilize this method.
http://help.yahoo.com/l/us/yahoo/mail/postmaster/postmaster-05.html
Whatever they call it is immaterial. The end result to our system is indistinguishable from real greylisting. Perhaps there's a tiny fraction that aren't ever deferred, but in general I find the majority of our queue is destined to @yahoo.com addresses. I think I'll followup on the other posters ideas of: 1) Implementing a separate outbound gateway just for yahoo.com 2) Advising users to switch to gmail.