I recently completed an installation of Exchange 2016 mailbox server into an Exchange 2010 environment, which includes one 2010 mailbox server and one 2010 Edge Transport server.
I created a test account on the 2016 database and tested the send/receive connectivity. I was able to send internally, but for external mail, it's hangs in the queue. Error below.
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Diagnostic information for administrators:
Generating server: Exchange2016.domain.local
Receiving server: edgesync - default-first-site-name to internet (2xx.xx.xx.xx)
example@Stuff .com
Server at edgesync - default-first-site-name to internet (2xx.xx.xx.xx) returned '400 4.4.7 Message delayed'
10/21/2020 10:43:36 AM - Server at edgesync - default-first-site-name to internet (2xx.xx.xx.xx) returned '451 4.4.397 Error communicating with target host. -> 421 4.2.1 Unable to connect -> SocketTimedout: Socket error code 10060'
Original message headers:
Received: from Exchange2016.domain.local (192.168.xx.xxx) by
Exchange2016.domain.local (192.168.xx.xxx) with Microsoft SMTP Server
(version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id
15.1.2106.2; Wed, 21 Oct 2020 02:46:10 -0400
Received: from Exchange2016.domain.local ([::1]) by
Exchange2016.domain.local ([::1]) with mapi id 15.01.2106.002; Wed, 21
Oct 2020 02:46:10 -0400