I have inherited an Exchange set up whereby a client is looking to migrate to O365 in the near future and the engineer who set this up has left me with the following;
Exchange 2016 Installed (blank database, no real config of the server performed)
Exchange 2010 current production MBX and CAS (all firewall rules and autodiscover point to this server).
Despite everything being pointed to Exchange 2010 (ie to ignore 2016) there are lots of issues with mailbox permissions and Outlook disconnects, where presumably 2016 is being queried with it being the later version and present in the AD forest. When all records and rules change to point to 2016, mailflow queues at the smart host (due to a TLS error connecting to the 2016 box). Hence this was pointed back to Exchange 2010.
My query is, will it create a problem to remove 2016 from the environment completely, to leave 2010, whereby i will then configure the Hybrid on 2010 to O365 without Exchange 2016 (i presume the previous guy installed 2016 as a Hybrid only server..). My concern is will it break anything given that the schema has been extended as part of the 2016 install with only 2010 present?
How i usually perform these jobs is to Hybrid 2010 to O365, Migrate and then once everything is moved across, install 2016 on a Hybrid license for Management Tools (no DB) before removing 2010.