Difficult to know without extensive coding in the QueryOpen event of the calendar view - in other words you have to change the mail template (not a good idea).
If you do need to know, you will have to install the Designer (I'm supposing you do not have it) and open your mailbox in it (if you have the authority to do so).
Once there, you will have to devise the necessary LotusScript or JavaScript code to get the necessary information.
In other words, there is no simple option to click on - you'll need a programmer to help you.
Pascal.