I am going to migrate from Exchange 2003 to Exchange 2010. The plan is to bring up the Exchange 2010 so it is simultaneously connected to the internet with the primary server to send and receive email. So for example, we will have:
Exchange 2003 WAN IP 126.96.36.199 LAN IP 10.100.100.2
Exchange 2010 WAN IP 188.8.131.52 LAN IP 10.100.100.3
The MX records will be:
Exch2003 MX priority 10
Exch2010 MX priority 20
I haven't setup 2 servers simultaneously before, but as I recall the Exchange environment relies on AD to route incoming emails to the appropriate mailbox whether it is on Exch2003 or Exch2010. Am I correct here? Will there be any problems if somehow emails comes into the Exch2010 first? I'm assuming it will move it to the Exch2003 and vice versa.
Lastly, does the 'routing group' that Exchange 2010 created when I installed it that pointed to Exch2003 have anything to do with this, or is it only between sites that this would be useful?