I'll defer to you on this. Clearly a failure to resolve is
not the same thing as a NXDOMAIN RCODE.
And yet, personal experience has show that the failure of all a
customer's DNS servers for a domain does cause swifter mail bouncing than
would occur otherwise. I do not know if it was due to the other providers
having broken MTAs or broken DNS servers/resolvers... Or maybe they were
all flukes. I now wish I had investigated them more thoroughly for the
few times I've seen it.
John
At 12:29 PM 9/29/2005, Todd Vierling wrote:
On Thu, 29 Sep 2005, John Dupuy
wrote:
> If you are talking about strictly http, then you are probably right.
If you
> are hosting any email, then this isn't the case. A live DNS but dead
mail
> server will cause your mail to queue up for a later resend on the
originating
> mail servers. A dead DNS will cause the mail to bounce as
undeliverable.
If a mail server is bouncing immediately on a DNS SERVFAIL (which is
what
you'll get when a remote DNS server is down), then that mail server is
badly
broken and will break quite a bit during tier1 failure
situations.
Failure to resolve != resolves to NXDOMAIN/empty. A failure to
resolve
(SERVFAIL) should result in the same queueing behavior that the remote
SMTP
server uses for failure to establish a TCP connection.
--
-- Todd Vierling <tv@duh.org> <tv@pobox.com>
<todd@vierling.name>