Up until a few months ago, when I created a new Microsoft Teams team, it would also show me a mailbox and calendar for the underlying O365 group in Outlook 2016/2019 and OWA. I then spent a lot of time baffled and trying to figure out what changed.
Finally I found the answer on a Tony Redmond post. Clutch as usual, thx Tony! The short answer was that Exchange Online has an O365 Groups setting called “HiddenFromExchangeClientsEnabled” that was used to be defaulted to false, but Microsoft changed it to default to true.
I get the rational…for most non-Exchange O365 services (Teams/Planner/others) default implementations/use cases (where there is no implemented governance controls on who can create a team/plan/etc.), users may not want/need or even understand that there is a mailbox tied to their new group when they create the team. The problem is that there are many use cases where access to the mailbox was intended/needed.
The only current solution I found so far to this issue is to create the O365 group in Exchange/Outlook first and then when creating the Teams’ team, use the existing O365 group. This however is a bit of a hassle and not at all practical in any organization where you want to allow users (non-IT staff) to create teams.
Others have proposed that Microsoft should allow the option to show the mailbox when creating the team in Teams (see User Voice post). I agree with this, but also wanted to find a way to add this option as part of an automated controlled Teams creation/governance process. Unfortunately other than using the Exchange PowerShell module, I haven’t found an API solution yet (including Graph/AzureADPreview). If someone knows of or finds one, please hit me up!!!
If you are running into this issue as well and you want to use the Exchance PowerShell module for now, I found a few articles on the interweb, but Tony Redmond’s is the best explanation and Morgan TechSpace has the most concise directions. Cheers.