Weird DNS issues for domains

Thu Sep 29 18:00:16 UTC 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.

The problem I've seen is when an SMTP server does not accept emails
which have non-resolvable MAIL FROM domain. When the sender is a dumb
SMTP client, not an MTA, this can cause problems.

(I noticed this happen to a high traffic customer who had both of their
DNS servers in the same /24 located in Slidell, LA. Needless to say, they
were down for more than a few hours when Katrina rolled through.)
-- 
Crist J. Clark                               crist.clark at globalstar.com
Globalstar Communications                                (408) 933-4387