Forum Discussion
Exchange 2010 and 2016 coexistence
- To see what is happening get the message headers and post them to exrca.com. This will show things like 2010 mapi to 2010 transport (as I described above) and later the last hop being to 2010. As the mailbox is on 2010, the transport service must deliver it to a Hub Transport role. 2016 cannot deliver to a 2010 mailbox. 2016 can deliver to 2010 transport but only 2010 transport can deliver to 2010 mailbox (as transport to transport is not version dependant but transport to and from mailbox is version dependant)
Hi Brian,
That is not what we have just experienced. With Exchange 2010 and Exchange 2016 installed in the same site, Exchange 2016 servers were picking up internal to internal messages for local delivery from the Exchange 2010 servers. The only way we noticed this is that the client had played around with the default receive connectors on the Exchange 2010 servers and restricted the remote server IP range, so the new Exchange 2016 servers weren't included. This caused messages to queue on the Exchange 2016 servers until they were allowed on Exchange 2010 receive connectors.
I believe this is due to shadow queue in Exchange 2010, or Safety Net in Exchange 2016. Exchange will always route an email through another Exchange transport server in the same site to create another copy of the message for backfill if necessary. See https://technet.microsoft.com/en-us/library/dd351027(v=exchg.141).aspx