Re: 550 5.7.1 NDR caused by Exchange using A record instead of MX
- From: "Slacker" <Slacker@xxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Sat, 28 May 2005 04:38:04 -0700
Thanks for the RFC reference David. If you think about it, falling back to
the A RR seems like a very bad idea. My case for example, the MX record is
not returned in the query because of timeout or whatever reason and then the
A record is queried. Can anybody think of a domain that has a website
without the www in front? There are quite a few. If that initial mx query
fails and the A record is queried, we are trying to send mail to the
webserver. Mail servers are so touchy anymore because of SPAM that servers
not using MX records probably fail to work with many servers. So in my
opinion, they should take that requirement out of the RFC?
Stephen
"David Strome" wrote:
> Exchange is required to query the A record if no MX records exist. See RFC
> 2821 section 5 for more information.
>
>
> "Slacker" <Slacker@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
> news:6D1692B2-9240-4943-A01B-7784765B0AF9@xxxxxxxxxxxxxxxx
> >I recently had a user report a 550 5.7.1 NDR to me. After researching the
> > error, I noticed that the message came from an SMTP server that was NOT
> > the
> > proper SMTP server for the domain domain.com. It was an an SMTP server
> > that
> > was running on the webserver for domain.com. The reason that it was
> > connecting to the webserver is that when it did a query for the A record
> > for
> > domain.com it got the IP address of the web server.
> > Both www.domain.com and domain.com have the same IP address.
> > Exchange should have queried the MX record for domain.com and not the A
> > record.
> > I browsed my DNS server logs which had debugging enabled and noticed where
> > the request was made.
> > I would like to know, why did Exchange query the A record??
> > I actually thought that is what it is supposed to do if it can't find an
> > MX
> > record but after thinking about it, that seems like a really bad thing to
> > do.
> > Unless a domain has an A record the same as the MX record, mail delivery
> > will
> > fail.
> > Is there anything I can do to prevent this problem like increasing the
> > timeouts for my forwarders or not allowing Exchange to fall back to A
> > records?
> > Any ideas would be greatly appreciated.
> >
> > Thanks,
> > Stephen
>
>
>
.
- References:
- 550 5.7.1 NDR caused by Exchange using A record instead of MX
- From: Slacker
- Re: 550 5.7.1 NDR caused by Exchange using A record instead of MX
- From: David Strome
- 550 5.7.1 NDR caused by Exchange using A record instead of MX
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