John,
I can see one way that a message might be returned with 'unknown user'.
As you know IMail tries MX records first and if all those fail, will try the
IP for the domain. So, if the MX hosts are down or unresponsive, then the
domains IP is tried (today, usually the web server, not a mail server) and a
SMTP server is found, IMail will attempt delivery. However if that mail
server (on the Web Server) is not configured to accept that domain/user, it
won't allow IMail to send, so IMail then bounces back to the sender, most
often with 'unknown user'.
This tells me the receiving domain is not configured correctly and at some
time had problems allowing connections to the MX hosts.
As most people today use the IP of their web server as the IP for the
'domain' (just so lazy people don't have to type www!), that host should
either not have a SMTP server (so no connection will be allowed), or if it
does, that SMTP server should be setup as a 'backup' server (accepts and
forwards to the MX host) for the domain. A few years back, the IP for the
domain was almost always the IP of the MX host and that is what I
recommended for a long time.
If you look in the IMail logs, you should see the error message 'MX fail
connect' prior to the delivery to the Web Servers IP. If there were no SMTP
service on that host, then IMail would have errored with 'Stack connect
fail' and requeue the message for later delivery.
Not your problem, but a problem with the receivers understanding of email
routing, DNS and misconfigured mail server on the web server.
As for your user, tell him to reply again and if the MX hosts are up like
you say, it should go through without trouble, this time.
Oh, one more thing, if there is an entry in the HOSTS file of the IMail
machine for that 'domain name', that would cause DNS to be bypassed and make
IMail connect to the IP found in HOSTS file. And if you tell us the domain
in question, then we can all look things over (DNS, MX hosts, etc...) to
verify what you see.
Daniel Donnelly
________________________________________________________
----- Original Message -----
From: "John Shacklett" <[EMAIL PROTECTED]>
To: "IMail Forum" <[EMAIL PROTECTED]>
Sent: Thursday, November 16, 2000 4:20 PM
Subject: [IMail Forum] chronic DNS unhappiness
> This subject has come up in the past, and I've [still] never come to an
> understanding of what's going on. Sometimes the issue turns up being DNS
> failures on the part of people I can't control, but this one I'm staring
at
> today baffles me anew.
>
> Forgive me for digging [pun intended] up old ground.
>
> One of my users tried to send a REPLY to a message that he received
earlier
> today. His reply came back "user unknown". The reply went to the SMTP
> service running on that domain's Web server, and not to the server
> represented by the DNS primary [and only] MX host.
>
> I ran a dig on the domain, and it reached both authoritative DNS hosts,
and
> got consistent responses from each. I believe that these domains are set
up
> correctly. I even ran the dig on MY ISP's caching nameserver, and got a
> perfect copy of the authoritative server responses. I ran a telnet session
> on port 25 of the MX host by domain name, not by address and not by host
> name, and got in fine. The reply-to address on that host verified. I
> checked the log for when the original message came in, and it came from
the
> MX host address. And I checked the log for the reply, and the "connect
> domainname.com" line clearly references the web server's address and not
the
> MX host address. And that WWW machine bounced the message, as it should.
>
> I have the dig results, the logs, the addresses, and a headache. This
> pattern repeats itself with increasing frequency. What experience are
other
> people having with this? I can share the details, but I think there's a
> deeper issue here that I'm not grasping. [Something that also repeats
itself
> with increasing frequency...]
>
>
> --
>
> John Shacklett
>
> www.continentaloffice.com
>
> [EMAIL PROTECTED]
> [EMAIL PROTECTED]
>
>
> Please visit http://www.ipswitch.com/support/mailing-lists.html
> to be removed from this list.
>
> An Archive of this list is available at:
> http://www.mail-archive.com/imail_forum%40list.ipswitch.com/
>
Please visit http://www.ipswitch.com/support/mailing-lists.html
to be removed from this list.
An Archive of this list is available at:
http://www.mail-archive.com/imail_forum%40list.ipswitch.com/
