Exchange 2016 co-existence with 2010 issue

Exchange migration from 2010 to 2016. I have been testing by moving some mailboxes over to 2016 server and switching incoming to new server but the incoming mail will not deliver to 2010 mailbox. If I have incoming port 25 going to 2010, mail sits in the queue for a bit then gets delivered to 2016. If I set port 25 to 2016 server, it sits in the "smtp relay to mailbox delivery group" queue and never gets delivered to the 2010 mailboxes. Am I missing some kind of connector?
Doug PennemanAsked:
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timgreen7077Exchange EngineerCommented:
Make sure there are no firewalls blocking communication between your exchange servers, especially the windows firewall.
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Todd NelsonSystems EngineerCommented:
If I were to make an educated guess, at some point, you probably customized the "Client" and "Default" receive connectors on the Exchange 2010 server.  I see this in almost all of the projects I have.  And hopefully, you didn't make any modifications to the receive connectors on the Exchange 2016 server.

First, document your Exchange 2010 receive connectors.
Second, set your receive connectors back to the default settings using this article ... https://oddytee.wordpress.com/2016/01/12/exchange-2010-default-receive-connector-settings/
Third, if you are relaying, use this reference to properly configure a "relay" receive connectors on both 2010 and 2016...
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Doug PennemanAuthor Commented:
Yes I tinkered with the connectors on the Exchange 2010. Who knew way back when that it would be a problem. Setting them back to default worked! Thank you!
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Doug PennemanAuthor Commented:
So now that I have the mail flow working, I tried moving a mailbox to the new server but Outlook will not try to connect to the new location. It is still looking for the old server (outlook /rpcdiag) and shows disconnected. I have autodiscover pointed at the new server and tried pointing it back to the old but no go.
I did this on another migration a few weeks ago and did not have this problem. Very similar setups.
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timgreen7077Exchange EngineerCommented:
open powershell on the exchange 2016 servers and run the following and see if that helps.

Restart-WebAppPool MSExchangeAutodiscoverAppPool
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timgreen7077Exchange EngineerCommented:
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Doug PennemanAuthor Commented:
It didn't work after about 5 minutes, so I rebooted 2016 and after a few minutes it connected. On to the next mailbox to see what happens. Of course I'm starting with the smallest mailboxes! thanks for your expertise.
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Todd NelsonSystems EngineerCommented:
Sufficient information provided to resolve SMTP issue.
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