We are upgrading Exchange 2010 – 2016. I am at the point of testing mail flow between the two servers. 2016 can send email to 2010 users and the Internet. But 2010 cannot send email to 2016 users. The email just sits in the queue until it times out. I ran the troubleshooting assistant and it says the root cause is that it cannot find a host record for the 2016 server. However there is a host record and I can resolve it from the 2010 server via ping and nslookup. I can also telnet from the 2010 to the 2016 server. Both servers are on the same network, same DC.
Exchange 2010 is on 2008R2 server and 2016 is on a 2012R2 server.
My plan is to migrate a small test group users to the 2016 server but to do that 2010 has to be able to send email to them. Any help appreciated