Teams MTR - External Access Approval

[Jeff Harlow]

We have a MTR device that needs to be able to accept 3rd party invites (Webex, Zoom, etc.). So I have Set-CalendarProcessing ProcessExternalMeetingMessages set to true.  However, I am curious, what are people doing to prevent spamming their MTR rooms since that pretty much allows anyone to send an appointment externally? 

[#2]

I mean you could always setup content rules etc. for them and only accept email from certain domains etc. if you have issues with people abusing them. But honestly the only thing that will get processed is calendar invites etc. so other spam shouldn’t effect them.

[#3]

Yeah, I noticed a post on the rules but that would only apply if you knew the domains that would be sending appointments (unless that would be the 3rd party). Cannot see that working unless you only had meetings with a selected few companies. I agree, it would only process invites. I am just thinking that this could become a target for malicious activity just to fill up calendar with a bunch of spam and cause problems.

[#4]

@Jeff Harlow I wrote a blog post here on securing the invites to devices Securing External Meeting Requests for Microsoft Teams Rooms | (graham-walsh.com)

[#5]

Hey Graham, I follow your page and saw this post. The question I have, do you have to whitelist the actual 3rd party service, say zoom.us or webex.com or the customer/client that is sending the invite? We have hundreds of customers and the domains changes daily, so I cannot just whitelist their domain but if it is the 3rd party service, that would be doable.

[#6]

That is correct, you whitelist the mail that contains say *.webex.com, so that can process the invite as valid.