550-Verification failed for myuser@mycompany.com ???

One of our customers has outsourced their mail to an IT services firm which apparently uses some kind of process to ensure "verification" and that the message is legit.

Our message fail on the error: "550-Verification failed for user XXX. 550-Previous (cached) verification failure 550 sender verify  failed 550-verification failed for XXX

I called their outsource provider and they refused to say anything other than: "Call Microsoft and tell them your your email is not verified".

I asked if they are talking about SPF records, or DNS.  They guy had no idea and just kept repeating the instructions to call microsoft or my ISP.

Any IDEA WHAT THIS IS ALL ABOUT?

We use exchange 2007 but use Mail Marshal in the DMZ to receive mail from the outside world, and ultimately to route exchange mail to the outside world.

Thanks,
Mike
mike2401Asked:
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arnoldCommented:
Your best bet is to check with the provider.
To better answer your question, at which point of the SMTP mail exchange session is that error reflected?
As soon as one connects.
After the exchange of greetings?
After authentication?
after identifying the sender?
after identifying the recipient/s?
after the sending of the message content?
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mike2401Author Commented:
It turns out there was a config error on the receiving party's email server.

However, this article describes what's going on:

http://en.wikipedia.org/wiki/Callback_verification

Turns out because we disable the Verify thing, (to prevent directory harvesting), this type of verification will indeed fail.

Ultimately, they added us to their white-list and now mail is flowing.

The first guy I spoke with at that company was completely un-helpful.
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mike2401Author Commented:
Thanks for responding,  I posted details on the verification in my comment, but am giving you the points because you were kind enough to reply.

Thanks.

_Mike
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