Consider the following scenario:
You send a meeting request to members of a Microsoft 365 or Office 365 organization or a Microsoft Exchange Server on-premises organization.
You are not a member of this organization.
You send the meeting request by using the event (iCalendar) format.
You specify a meeting organizer in the mail address of the P1 header.
In this scenario, the details in the P1 header are ignored.
Example: You send a meeting request from your personal email account. The meeting organizer could be anyone. However, Exchange ignores the details in the P1 header field and displays the sender of the request (you) as the meeting organizer.
To fix this issue, install the following security update: