If you have not used webinars in Microsoft Teams yet, you need to configure some policy settings. Webinars are enabled in your tenant by default, but the ability for external people to register for your events or view the engagement report is disabled. Meetings support up to 1000 attendees for enterprise customers and 300 attendees for M365 Business Premium customers, but the overflow setting is disabled by default. At GA these settings could only be configured using PowerShell, here is how you do it.

#Install latest Teams PowerShell module
#The force switch enables you to install the newest version if you have an older version already installed
Install-Module MicrosoftTeams -force

#Connect to Microsoft Teams
#Minimum requirement is that your user is enabled with the Teams Communications Administrator Role
#Teams Administrator and Global Administrator role works too
Connect-MicrosoftTeams

#Default config
Get-CsTeamsMeetingPolicy | Format-List Identity, AllowEngagementReport, WhoCanRegister, AllowPrivateMeetingScheduling, StreamingAttendeeMode 

Identity                      : Global
AllowEngagementReport         : Disabled
WhoCanRegister                : EveryoneInCompany
AllowPrivateMeetingScheduling : True
StreamingAttendeeMode         : Disabled

#New config
Set-CsTeamsMeetingPolicy -Identity Global -AllowEngagementReport Enabled -WhoCanRegister Everyone -AllowPrivateMeetingScheduling $True -StreamingAttendeeMode Enabled

#Result
Get-CsTeamsMeetingPolicy | Format-List Identity, AllowEngagementReport, WhoCanRegister, AllowPrivateMeetingScheduling, StreamingAttendeeMode 

Identity                      : Global
AllowEngagementReport         : Enabled
WhoCanRegister                : Everyone
AllowPrivateMeetingScheduling : True
StreamingAttendeeMode         : Enabled

Now you are ready to run public webinars, get the engagement report and even have more than 1000 attendees using the overflow to live event feature from user number 1001. You may want to create a separate Teams Meeting Policy for those booking webinars, and not user global as I have done in the above example.

In our environment we were running on AllOn built in policy and it turns out that you cannot set this setting on built in policies, only on custom policies and Global. Also the AllOn MeetingPolicy is depricated so do not use that one. If you are like us, using an old built on policy and want to set global Teams meeting policy, you can either do it manually per user in the Teams Admin Center or you can use powershell and loop through users and revert back to the global policy. If you are not specifying a UPN in the below command, it will loop through all your users and set global policy on all of them, be careful when doing this in production. Setting the policy to $Null will revert you back to a global policy.

Get-CsOnlineuser <UPN> | Grant-CsTeamsMeetingPolicy -PolicyName $Null

Fellow Office 365 for ITPros author, Tony Redmond has a well written blogpost explaining the settings in detail. Teams Meetings Get Webinar Capability (practical365.com).