I run a hybrid exchange environment with Exchange 2016 and Exchange Online. I have a maintenance event coming up with my on-premise exchange server where it will be offline for a few days. I have 2 questions:
1. My on-premise exchange 2016 server still currently houses all my distribution groups that are internally and externally available. All of the user mailboxes are in Exchange Online. If I shutdown the Exchange 2016 on premise server, will the distribution groups still work if my hybrid setup is configured properly? 2. If I flip my mail routing to flow through Exchange Online first, will exchange online deliver messages with a destination for the on-premise exchange server?
It depends on how you are routing the messages and whether the groups are synchronized to O365. If the message is handled by ExO and the group is represented by a recipient object there, it should be expanded/resolved to the individual recipients and delivery will work.