Hi all, I've created a new exchange mailbox on-user with on-prem mailbox and then migrated it over the 365 and all looks and works fine.
I have then added 5 users to the permissions list of that mailbox and can see the permissions have applied with powershell but it seems that users that use Outlook 365 can see the mailbox in Outlook - if they user Outlook 2016 the mailbox doesn't appear in their list. If they add the maibox manually it does get listed but then they get a folder error. I can see the mailbox fine and it popped into my Outlook 365 client without issues.
Do we need to upgrade everyone ?
