Exchange 2010 side-by-side upgrade delayed delivery

Doing a side-by-side upgrade to Exchange 2010. I have users on Exchange 2007, some are already moved to Exchange 2010. I relay mail via a smart host (hosted SPAM filter solution)

- Users from Exchange 2007 can send/receive emails externally and internally
- Users from Exchange 2010 can send externally/receive externally and receive internally BUT

Problem is Exchange 2010 users cannot reply or send internally to Exchange 2007 users.

Am i missing a connection between 2010 and 2007 until i finish moving everyone over?
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vaworxConnect With a Mentor Author Commented:
Thanks for your input JuusoConnecta,

I finally managed to fix the problem myself. It all boiled down to 8 ACL lines on my border router that i needed to add as a list of allowed IPs to port 25 on the new server's public IP. Also had to add my new Exchange 2010 IP to the Old Server's Default Mail receive connector rule, Network tab (receive mail from remote servers that have these IP addresses).

Bouth exchange servers in the same root domain ?

What is the NDR ?

Can you tryck those messages from exchange 2010 EMC and see where they are stuck ?

vaworxAuthor Commented:
Same domain, side by side upgrade both servers serve the same

The message says:

Delivery is delayed to these recipients or groups:

User (

Subject: RE: testing @ 5:44pm

This message hasn't been delivered yet. Delivery will continue to be attempted.

The server will keep trying to deliver this message for the next 1 days, 19 hours and 54 minutes. You'll be notified if the message can't be delivered by that time.
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vaworxAuthor Commented:
Some more details on the subject. The hosted SMTP is with Symantec MessageLabs. I've added the new public IPs in there already.

the MX servers are the relay servers from MessageLabs.

Here is some more tracking info:

Delivery Report for  User ¿(¿

11/15/2010 5:40 PM
The message was submitted to
11/15/2010 5:40 PM
The message has been queued on server '' since 11/15/2010 5:40:29 PM (UTC-10:00) Hawaii. The last attempt to send the message was at 11/16/2010 2:22:23 PM (UTC-10:00) Hawaii and generated the error '451 4.4.0 Primary target IP address responded with: "421 4.3.2 Service not available, closing transmission channel." Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts.'.

11/16/2010 2:30 PM
Message delivery is taking longer than expected. There may be system delays. For more information, contact your helpdesk.
Havent worked with Symantec MessageLabs, but looks like something is blocking them.

It looks like the message is trying to take an route to the web and back in onto your organization instead of having the mail routing go internally, which should be by default since bouth exchange servers are within the same domain..
vaworxAuthor Commented:
Solved it myself.
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