On Wednesday, August 7, 2002, at 05:54 , Simon Byrnand wrote:
However if the reverse DNS for end users (eg, dialup, Jetstream, and so forth) is broken in such a way that the DNS times out instead of immediately failing, this can pretty much kill email for those end users.
When the user connects to the mail server, most MTA's (Sendmail certainly does) try to do a reverse lookup on the clients address. If that failed immediately then there wouldn't be a big problem, but if the nature of the dns failure means that every single lookup has to time out, (typically a couple of minutes) then the mailserver wont respond with its welcome banner until after that timeout.
So use an MTA which allows you turn off the PTR lookup. There, that wasn't hard. Next! Joe - To unsubscribe from nznog, send email to majordomo(a)list.waikato.ac.nz where the body of your message reads: unsubscribe nznog