Exchange 2003 on Server 2003 DC - Added Server 2008 R2 DC....

I have an Exchange 2003 SP2 server on Server 2003 that is a DC and DNS server. I have 3 domains and a few users use POP3 to get mail from outside my network which works fine. When they try to send mail from outside my network they can't authenticate.
This worked until I added a Server 2008 R2 DC to the network yesterday. The server 2k8 machine only has AD and DNS installed on it.
No issues with AD synchronization between them.
All other mail seems to be working fine.

Is there something in the authentication with Server 2k8 R2 that could be causing this to fail?
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Kevin HaysIT AnalystCommented:
Rather than type all this out, I will post a link that talks about 2003 exchange and 2008 R2 server.  At first I did not think 2003 would work at all with a 2008 domain and this might shed some light on your problem.

ljlkrlAuthor Commented:
That is probably  the problem. I know the only thing that changed was adding the 2k8 r2 DC to the mix.
What is the solution other than upgrading to Exch 2010 sooner though?
My ultimate goal is to transition to Exchange 2010 and that is why I added the 2k8 DC. It just seems strange that I can use a test account on my iphone connected to my internal wifi and on a laptop using the same settings from inside my network with no problems. If I try the  with an external internet connection or the iphone 3G the connection it fails.
OWA to the exchange 2k3 box works from outside too.

They mainly use their iPhones for outside mail, so I tested setting up a second exchange account on my iphone and it works fine.
I think this is how we will handle this so I can move on with the Exchange upgrade.

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ljlkrlAuthor Commented:
I read the link you posted again, and looking at the Exchange Supportability Matrix here:
I see no reason why running Exchange 2003 SP2 on a Server 2003 SP2 box with a forest and domain level of Server 2003, and a Server 2k8 r2 AD would be a problem.
The matrix says it is supported.
Kevin HaysIT AnalystCommented:
I have the opposite problem with iphone 3/4 with inside the domain.  People can get their email from outside the domain, but if they are in they cannot.  My clients are using 2003 and/or 2007 exchange also.

Good luck on the upgrade.

ljlkrlAuthor Commented:
No real solution to question answered. I found a work around for it.
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