Unable to join forwarded External Teams Meetings to MTR

jameshamilton 

Thanks for the detailed response.

The Mimecast rule is all set up and I can that there is no rewrite when hovering over the Teams Invite link.

The issue for me is as follows where the organiser is external to the Company.

Scenario 1

Before accepting the meeting, the INBOX message invite is forwarded to the Meeting Teams Room (MTR).

The invite is accepted by the MTR and recognised as a Teams Meeting (Teams icon present).

Scenario 2

The INBOX message invite is accepted and an entry appears in the users calendar. The original message in the INBOX disappears.

The meeting invite is forwarded via the calendar entry, but the MTR does not accept the forward and no entry appears on the MTR as a result.

In your environment, do both scenarios work?

Chris-Yue If it helps, this is the method I used, which works perfectly:

• Administration -> Gateway -> Policies
• Definitions -> URL Protection
• Managed URLs
• Add New Managed URL, with the following settings
  • Override Type = Permitted
  • Disable rewriting for this entry = Ticked
  • Match Type = Domain
  • URL(s) = https://teams.microsoft.com/

The PowerShell command is only needed if you want the calendar to be able to auto-accept, via the auto attendant service, invites from external senders and is nothing to do with the problem you're experiencing. It just somehow got mixed up into this thread.

jameshamilton I am using Mimecast and am experiencing the same issues when forwarding a MS Teams invite to a Meeting Teams Room device.

I have disabled URL rewrite on Mimecast in 2 places:

Administration > Services > URL Protection Bypass

Administration > Gateway > Polices > URL Protection Bypass

I can now see that the URL is no longer rewritten but this is still not working.

Join on the web URL is still being rewritten but I did not think that was important.

Also, when forwarding a Teams invite from a company user to the MTR do I still need to run the following PowerShell command?

Set-CalendarProcessing -Identity email address removed for privacy reasons -ProcessExternalMeetingMessages $True