I'd like to understand a few more things about mail flow and coexistence in our 2010/2013 environment.
Emails from users on Exchange 2010 are being routed through the 2013 mailbox servers now to get to the internet, via our edge transport server. Why are they going through 2013, and not going out straight from 2010?
Also, any users with mailboxes on 2013 cannot send emails out to the internet. When I telnet to the edge transport server to send an email, I get the error 550 5.7.1 Unable to Relay. When I checked the logs on the edge transport server that I telnetted to, I saw this:
Received certificate 2015-01-26T11:47:08.401Z,edge01\Internal_Mail_Servers,08D2050B356B6D47,27,192.168.2.2:25,192.168.1.2:22221,,,<THUMPRINT>,Certificate thumbprint 2015-01-26T11:47:08.401Z,edge01\Internal_Mail_Servers,08D2050B356B6D47,28,192.168.2.2:25,192.168.1.2:22221,,,DirectTrust certificate failed to authenticate for CN=EXMB2013_01