Guest accounts added as members of Office365 Groups are subscribed to emails regardless of group's AutoSubscribeNewMembers setting

Question

When I add guest users to Teams-enabled Office365 Groups, they're getting subscribed regardless of the group having AutoSubscribeNewMembers being set to False.

My process for creating a new Team:

1. Create an Office365 Group that is Teams-enabled, adding only Owners - not members.
2. Edit the group settings to allow email from external senders.
3. 'Send copies of group conversation and events to group members' NEVER gets checked.
4. Add members, both internal and guest.

At this point, an email from an unrelated third-party sender will land in the group mailbox successfully (as expected), not get forwarded to Internal group members (as expected), but will get forwarded to Guest group members (this is the problem).

Powershell Get-UnifiedGroup confirms that AutoSubscribeNewMembers is False, AlwaysSubscribeMembersToCalendarEvents is True, and SubscriptionEnabled is True - which I believe is the default setting when you don't check the 'Send copies' box from step 3 above.

However - The moment I add a guest account as a member to the group, Get-UnifiedGroupLinks confirms that they're also a subscriber. I can remove them as a subscriber, but this seems like I shouldn't have to if AutoSubscribeNewMembers being set to False was being respected.

Is there another setting somewhere that could be superceding the group's AutoSubscribeNewMembers setting? Does that setting only apply to Internal members and not Guests?

Answer 1

Microsoft support confirmed this to be the 'expected' behavior.

The AlwaysSubscribeMembersToCalendarEvents, AutoSubscribeNewmembers, and even SubscriptionEnabled attributes only apply to internal user accounts, not guest user accounts. Guest users are always subscribed to Groups regardless of the group's configuration.

It's worth noting that Guest account subscriptions can be reviewed and manually removed via Get-UnifiedGroupLinks powershell cmdlet (and I'm sure there's a Graph API solution), but as of this writing there is nowhere in the Office365 Admin UI to view or manage these links, and they must be manually currated each time a guest user is added a group.