Exchange 2010 -> 2016 Migration: internal Mailfow

Hi,

I know this has been talked about a million times and more, but I can't find my error in this one:

Exchange 2010 SP3 on Server 2008 (R1) hosting roughly 450 mailboxes alone.  New VM 2012 R2 running Exchange 2016 CU3 just installed into the domain.  All seems well.

I can mail from 2010 to 2016, but not the other way.  The messages stall in the queue on the 2016 box with this message:

[{LRT=20.11.2016 12:50:01},{LED=451 4.4.0 Target host responded with: "451 5.7.3 Cannot achieve Exchange Server authentication." Last endpoint attempted was 192.168.5.104:25};{FWDN=internal.domain.local};{192.168.5.104}]

The IP is the one of the old box.  I checked the receive connectors and disabled Exchange Server authentication on every one.  I also checked the send connectors on the 2016 box and disabled it there.

Where else can I look?
LVL 2
Ralph ScharpingDigital TherapistAsked:
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Pune TechCommented:
Please refer following article to fix this issue

http://www.petenetlive.com/KB/Article/0000791
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Ralph ScharpingDigital TherapistAuthor Commented:
Looks like what I missed was a restart of the transport service...
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Pune TechCommented:
Thanks for the update and points.
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