In a Windows 2003 environment, there is an Exchange 2003 mail server. All mailboxes have now been successfully migrated to 365. There is active directory integration provided by an on premises DirSync server.
The Exchange server is still available on the network, but Exchange is no longer actively used. 2003 Administrative Tools are installed on the Exchange server and facilitate the creation of new accounts, distribution groups, general administration with the availability of the features highlighted in screenshot 1.
Screenshot 2 was taken from a domain controller (not the Exchange server), which indicates that the Exchange tabs are not present.
With the above in mind, and anticipating that administration may need to be conducted directly form 356, we added an alias directly from the 365 portal and were presented with the message indicated in screenshot 3
We want to decommission the on-premises 2003 Exchange server from the network so we can upgrade the domain from 2003 to 2012
When we fully uninstall the on-premises Exchange server this effectively decommissions Exchange from the internal domain, what measures do we need to take to ensure we do not lose administrative functionality of mailboxes, distribution groups, contacts etc..