I could be wrong but there does not seem to be a built-in functionality that
would support this activity. What you are talking about is "data mining" or
"data extraction" because each message in Outlook represents its own "record"
in the database that is your "Mailbox - ".
It would probably take a third-party or add-on application to get this
information out of Outlook and even before that it would be necessary to get
copies of all the "Sent Items" messages into a .PST file. The .PST file is
locally stored on your hard drive and therefore a little bit more accessible
for "opening it" and looking at the data.
The .PST file is considered as "in use" when Outlook is opening and running,
so the only way you will be able to examine its contents would be with the
Outlook program closed.
Also, keep in mind that the "structure" of this file is almost certainly a
proprietary Microsoft design, so any third-party tool you find will be what I
would call "Advanced" in its features.
You should always make a Backup Copy of any file before working on it in
order to prevent corrupting the master file.
If someone else on within the "Outlook General Questions" group has a more
specific suggestion, wow! This really seems like a rather sophisticated task
you have chosen for yourself so I will just wish you luck with that.
~