You can easily add people from outside your Office 365 tenant to the membership of Teams, but some oversight of who those people are and what teams they join is probably needed. This PowerShell script shows how to find records in the Office 365 audit log and figure out if they relate to the creation of new guest accounts before sending email asking to justify the addition of the new account.
The combination of Exchange Online and PowerShell allows Office 365 admins to send messages for all manner of reasons. These scripts depend on SMTP AUTH connections and change is coming in this area with the deprecation of basic authentication. It’s a good idea to take an inventory of scripts that send email, including those that use the .NET classes to do the job.
Office 365 Activity Alerts don’t seem to be working too well these days. At least, that’s what we found when we tried to create an alert for Teams creation events. Never mind, PowerShell will do the job as we can quickly whip up a PowerShell script to find audit records for team creations and put them into an email.
You can use the Send-MailMessage cmdlet in a PowerShell script to send mail messages via Exchange Online. And sometimes your IP address might be listed as a spammer, which is bad. All in all, authenticated client submission seems best.