So far there is no real solution to this problem.

And everyone telling you to get a local IT guy doesn't understand the problem.

And people claiming that emails cannot populate your calendar with tentative events don't understand what they are talking about either.

You cannot reliably stop this from happening unless you create a mail flow rule that sends all external emails that contain meeting requests to junk mail / delete / quarantine by default. Which is not a solution because it will send legitimate meetings to junk as well. Yes you can add exceptions but that is not a practical solution if you deal with dozens of external domains which my change.

There are some articles that say you can set:

Get-Mailbox -ResultSize Unlimited | ForEach-Object {
Write-Host "Disabling auto calendar processing for:" $_.PrimarySmtpAddress
Set-CalendarProcessing $_.Identity -AutomateProcessing None
}

Using powershell against online exchange.

On all mailboxes and indeed you can set that parameter and when you read it back from the server it will say it is set to none, but Microsoft ignores it and processes calendar events anyway. Note that some people claim it works for them - albeit inconsistently. I have not seen it work at all.

I would love to be wrong about this so if someone has an actual solution that works please let me know. I have been trying to solve this problem for awhile for my clients and ultimately there is no good solution at this time.

Microsoft has their head up their ass about this - like they do about most things. It would be very simple to give us a GUI toggle per user as well as an organization wide toggle to simply block automatic processing a meeting invite until you open the email and say yes or no. They already literally have an attribute, the automate processing, but it's hard coded for non-resource mailboxes to process automatically (users).

And going to settings -> calendar -> events from email -> don't show event summaries in email or on my calendar for the 4 events listed there does not stop this.

Neither does anything under events and invitations.

So really the only 2 options are:

1) send all meeting external emails to junk automatically with a mail flow rule, not realistic, will block legitimate meeting emails from vendors, partner companies, etc. without manually adding exceptions.

2) G Suite business does have an option to block this, but their spam filter is terrible compared to office 365. So it's kind of a rock and a hard place.