If you’re running Exchange in hybrid mode, there’s a big gotcha with Office 365 Groups and the ability to display them in Outlook 2016.
Normally, any Office 365 Group a user is a member of, will show at the bottom of their mailbox folders under a section called ‘Groups’. The user doesn’t have to do anything, they just show up.
However, as covered in this Microsoft Support article, when using a hybrid setup between Exchange on-premises and Exchange Online, Office 365 Groups won’t show in Outlook when the email address of the group is anything but “@contoso.mail.onmicrosoft.com” (with ‘contoso’ being your Office 365 tenant name).
Many people configure their primary email domain the same as the UPN, which is then the same as their default Office 365 domain. When you create an Office 365 Group through the Office 365 Admin Center (which is now renamed to the Microsoft 365 Admin Center), the domain for the email address has a drop down arrow, but is greyed out so can’t actually be changed – it will only show you the default domain:
If you create an Office 365 Group this way, it won’t show for Outlook 2016 users in a hybrid setup. You can adjust the email address with a PowerShell command afterwards as per the Microsoft Support article:
Set-UnifiedGroup Alias -PrimarySmtpAddress <Office365GroupName>@contoso.mail.onmicrosoft.com
Where ‘Alias’ is the mailbox alias, and should match what you typed into the ‘Group email address’ field. Make sure you’ve got your own tenant in the email address domain rather than ‘contoso’ too.
Alternatively, you can create the Office 365 group in PowerShell, or use the Exchange Admin Center to create an Office 365 Group:
On this page, it’s possible to drop down the domain option and choose your ‘contoso.onmicrosoft.com’ option.
For someone starting out with Office 365 Groups, this could be an easy one to overlook as you’d expect to create everything with your preferred domain, and for it all to ‘just work’.