Mystery Emails for Meeting

Hello

I have this weird issue that I have been tracking down.

A user's mailbox sends emails out every night as reminders to an appointment that they setup. The email goes to all participants in the meeting, regardless of whether they accepted or not. I used message trace to track the source IP and it trusted, none network within my management, which wouldn't have devices unaccounted for.

I am not concerned that it is malicious or an account takeover situation, since there isn't any content added to the meeting. It is the same email every morning this week.

Is there a cause for this? Are there any options in Exchange or outlook that this could be attributed to? For example one that would effectively say "keep reminding participants of this"?

A few other details, which may or may not be relevant:

On at least one occasion, I verified that their computer was turned off. So, it is either their iPad or there iPhone, but I am not sure if that is relevant. I have this posted to an apple forum as well.

Of the 6 participants that the message goes to (according to exchange message trace) only 1 actually says that it shows up in his mailbox. Which makes me think that the other mailboxes are simply processing the redundant meeting message and there is something special about this one. But, I don't want to focus on that because it is too dependent on user input. It's really a question of why the messages are being sent in the first place.

Thanks!

This is a weekly recurring meeting and these mystery emails are going out daily.