From time to time I notice that typically end-user complaints for involuntary meeting request appears in his mailbox. There could be many reasons for this issue. Here is one thing that should be known, if you will troubleshoot similar issue. The thing is delegate access.
Who is the dalegate?
Similar to having an assistant help you manage your incoming paper mail, you can use Microsoft Outlook to allow another person, known as a delegate, to receive and respond to meeting requests or responses and to send e-mail messages on your behalf. You can also grant additional permissions that allow your delegate to read, create, or have full control over items in your Exchange mailbox.
Turn on Delegate Access?
It can be allowed via Outlook look at this post.
How is involuntary meeting request related to delegate access?
If a delegate needs permission to work with meeting requests and responses only, the default permission settings, including “Delegate receives copies of meeting-related messages sent to me“.
How to check delegate access for particular mailbox via Exchange Management Shell?
Get-Mailbox -anr "user name" | Get-CalendarProcessing | select ResourceDelegates
How to remove all delegates from particular mailbox?
Get-Mailbox -identity "alias" | Set-CalendarProcessing -ResourceDelegates $null