I'm hoping that someone from Xtra can advise exactly what is going on.
Michael
As Craig said previously it looks just like basic greylisting (http://en.wikipedia.org/wiki/Greylisting), nothing sinister and nothing they are going to explain more. Whilst all the reputational suggestions before are useful I doubt they have any effect at all because greylisting doesn't use them.
regards Jay
Hi Jay, If you actually search for the specific error (4.16.50) on the URL given i the bounce, the result is this: http://help.yahoo.com/l/us/yahoo/mail/postmaster/errors/postmaster-21.html Note it specifically uses the phrase "emails from your mail server have been generating substantial complaints from Yahoo! Mail users" - ala people are hitting the 'report as spam' buttons and some internal Yahoo magic is being applied to the IP as a result. The page further suggests the use of this form to report "if you're seeing this error consistently over an extended period of time" - http://help.yahoo.com/l/us/yahoo/mail/postmaster/defer.html . Whenever this comes up, someone mentions Greylisting. Greylisting delays are usually in the minutes; one assumes that by the time it's posted to NZNOG, the delays have become more noticable than that.[1] Given the number of times Yahoo and these sorts of errors have come up online before[2][3], i'd see it as far more of a reputation issue, to be honest. Andy D's post makes a lot of sense. Mark. [1] Yes, I know, risky assumption on occaision... [2] NZNOG at the following links: http://list.waikato.ac.nz/pipermail/nznog/2008-December/014891.html http://list.waikato.ac.nz/pipermail/nznog/2007-August/013401.html http://list.waikato.ac.nz/pipermail/nznog/2007-October/013526.html [2] NZLUG at the following link: http://www.linux.net.nz/pipermail/nzlug/2008-December/014926.html