Unable to join forwarded External Teams Meetings to MTR

Copper Contributor

Hi Everyone


We have an issue whereby the MTR does not allow you to join any forwarded external Team meeting invites.   The resource mailbox will accept the invite however when you go to the meeting room the JOIN button is not there.


If the invite is sent directly from the external we will be able to join the meeting in the MTR.


We use Crestron Flex.   We have changed the settings in Proofpoint so that the URL is not overwritten, enabled the resources to accept/decline external meeting invites however we are still having the same issue.   


Any help would be greatly appreciated.

23 Replies
This could be to do with Transport Neutral Encapsulation Format (TNEF). I thought this issue was largely resolved but it may still be related. These articles might be helpful - http://blog.schertz.name/2019/08/exchange-resource-mailbox-configuration-for-meeting-rooms/. https://docs.microsoft.com/en-us/skypeforbusiness/deploy/deploy-clients/room-system-and-federated-pa... Set-CalendarProcessing -Identity ABC@Contoso.com -DeleteComments $false New-RemoteDomain -DomainName Contoso.com -Name Contoso Set-RemoteDomain -Identity Contoso -TNEFEnabled $true Let me know how you get on.

@MJBuxton When I'm using Outlook application and forward to MTR systems I always remove the text in the top of the message since I had the same problem as you a long time ago when I didn't remove this text. I'm not sure if you have to remove that anymore and I rarely use Outlook application (use web app instead) so I can't say for sure.

Linus Cansby_0-1597439526219.png


Sounds like the invite is getting messed up. This can also happen for Guest Join Access for Webex. Check out the docs here https://docs.microsoft.com/en-us/MicrosoftTeams/rooms/third-party-join
Thanks everyone. We found that we had to turn this on which means that externals can book your meeting rooms <sigh>

@MJBuxton What exactly did you turn on?

@MJBuxton I'm having the same issue.

What exactly did you turn on?

@Askanison  Set-CalendarProcessing -Identity YourResourceMailboxMailid@YourDomain.com -ProcessExternalMeetingMessages $True  -  It will enable external domain to book your organization's meeting room.

What do you mean by removing the message at the top?
Sorry to resurrect an old thread but I think there is some confusion about the issue at hand here.

The OP complained that forwarded invites result in the meeting room kit not resolving the fact that it's a joinable meeting. The first suggestion may fix this, although I can't verify right now.

The ProcessExternalMeetingMessages flag is completely separate and simply enables the mailbox associated with the meeting room kit to automatically accept calendar invites, exactly as it would for internal invites.

Did anyone successfully fix the problem the OP had? I'd be interested to hear as this causes us massive grief.



Hi James,

We are having the same issue, we can't join external forwarded meetings.


Did you ever find a solution?





Sorry, never managed to resolve this and the only way round it is to forward the invite via 'Outlook on the Web', which we don't use due to a lack of integration with our other desktop products.





Thank you for your reply, I looked through a lot of forums for a solution and could not find anything that would work, I opened a case with Microsoft, slim chance they will figure it out.

I opened a case with Yealink and they are pointing me to forums, what can I expect for a company based in China.

I will let you know if I find anything that works.


@yeslink  I was able to resolve this, I can't recall what the issue was as it was a while back, but I'll check back my notes to see. Most likely it was something in powershell.


I did set it up as a hybrid Exchange, created the MTR accounts as resource accounts, set  it to auto respond to requests. The forward must be an actual meeting invite.

@MrSaltyTT It would be really to know what you did, if you're responding to the OP's actual issues.


Processing external calendar invites isn't a problem but invites that have been forwarded on to the equipment/device is where the problems occur. The equipment/device doesn't detect them as Teams meetings so you can't actually join the meeting.

Finally figured it out, our email spam protection service was modifying the links inside the Teams meeting invite forwarded, therefore the room was not recognizing the meeting as a Teams meeting so no Join button was showing up. Until they have a fix we are going to bypass the filter for the forwarded invites.
Glad you did. We had that issue as well and had to make an exemption for Teams and the other supported invites i.e. Zoom and Webex

@jameshamilton when you forward an invite to the room, what does the url show in OWA for that room mailbox? Is the URL modified or is it teams.Microsoft.com etc?

This worked a treat. Disabled URL rewriting for teams.microsoft.com links in Mimecast. Cheers!

@joeyturner I'm about to try this with our environment now and will feedback the results.