Exchange mailing to A records intermittently instead of MX records ???

We are experiencing very bizarre stuff on our exchange servers when mailing
to external domains.

SMTP delivery is working fine and then all of a sudden we start getting
failure reports back.
We've been digging around and tracking, and we find that all of a sudden the
SMTP virtual server is trying to deliver to the IP address of the A record
for the domain, instead of to the IP address of the MX record. As in most
cases this is the web server, we get a response back indicating that the
server cannot relay for that domain, which is normal.

My question is: why does the SMTP connector decide to send to the A record
all of a sudden, instead of to the MX record ???
Can we tell exchange to only attempt mailing to MX records ?

I looked into the DNS caches and the information is correct.
I ran DNSDIAG on our Exchange servers, against the various destinations and
on the various virtual SMTP servers, and they all come back with the
appropriate MX information. I don't know where to look anymore.

BTW: after awhile it will revert sending to the MX records, as if nothing
happened ...

Our Exchange servers are multihomed systems. There is a single SMTP Virtual
Server (VS) connector for each NIC. The SMTP VS on the external connector
looks at our internal DNS servers, while the SMTP VS on the internal
connectors looks to external DNS servers. (Setup according to one of MS's KB
articles).

Any ideas ?

Thanks.
Denis.



.

Relevant Pages

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