Relaying Error? No answers to be found!

The following recipient(s) could not be reached:

      joeschmoe@this.com on 6/23/2006 12:30 PM
            There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.
            <exchange.that.local #5.5.0 smtp;550 Relaying is prohibited>


Sending from "that.com" to "this.com" is sending back this error.  All sides have Exchange 2003 with SP2.  We also have problems this "that2.com" sending to "this.com"

"this.com" can send to "that.com" and "that2.com"

I think it is something with IMF but I am just not sure.  Wwe ("this.com") are getting email from all other people but a certain few domains....

Any ideas?
lttechAsked:
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SembeeConnect With a Mentor Commented:
Could be replication time.
The old ISP may well have switched off support for your domain immediately, before the change has replicated around the internet.

Changing ISPs needs to be carefully managed - preferably involving the current ISP as little as possible.

Simon.
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SembeeCommented:
It will not be IMF causing that message. If IMF had blocked a message you would get something else.

Do you have anything else installed on the machine that could be scanning the email traffic? I have seen third party applications reject messages with a similar message.

Simon.
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lttechAuthor Commented:
Sembee,

Nothing at all.  It actually all just came about once we switched to a new ISP.  I had them point Reverse DNS to the proper address, but I still get a report that reverse DNS is not configured for our server.
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ECNSSMTCommented:
hmm, I wonder if this will disappear in 48 hours after the DNS and MX record change..  I also wonder if your previous ISP had an SMTP relay setup just right before email hits your email server.

Regards,
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