You can search for recent Sent Items on the server using something like this:
cd /home/e-smith/files/users
find . -ctime -1 |grep -i sent
* -ctime -1: find all files created in the last 1 day
* grep -i sent: include in the output anything containing "sent", ignoring case (-i)
I've seen different email clients use "Sent", "Sent Items" and "Sent Messages". If I change "-ctime -1" to "-ctime -10", I see that I have all three of these on my account:
./support/Maildir/.Sent Items
./support/Maildir/.Sent Items/maildirfolder
./support/Maildir/.Sent Items/tmp
./support/Maildir/.Sent Items/new
./support/Maildir/.Sent Items/dovecot-uidlist
./support/Maildir/.Sent Items/dovecot.index.log
./support/Maildir/.Sent Items/dovecot.index.cache
./support/Maildir/.Sent Items/cur
./support/Maildir/.Sent Items/cur/1527351935.M478949P8602.office,S=7396,W=7528:2,S
./support/Maildir/.Sent Items/cur/1527350066.M257951P5934.office,S=1223,W=1265:2,S
./support/Maildir/.Sent Items/cur/1527350029.M591954P5878.office,S=699,W=724:2,S
./support/Maildir/.Sent Items/cur/1527601499.M711966P8065.office,S=7090,W=7247:2,S
./mmccarn/Maildir/.Sent Items
./mmccarn/Maildir/.Sent Items/tmp
./mmccarn/Maildir/.Sent Items/dovecot-uidlist
./mmccarn/Maildir/.Sent Items/dovecot.index.log
./mmccarn/Maildir/.Sent Items/dovecot.index.cache
./mmccarn/Maildir/.Sent Items/cur
./mmccarn/Maildir/.Sent Items/cur/1527707147.M277894P22460.office,S=39516,W=40289:2,S
./mmccarn/Maildir/.Sent Items/cur/1527352381.M370254P8981.office,S=8841,W=8993:2,S
./mmccarn/Maildir/.Sent Items/cur/1527945032.M147900P7953.office,S=1253,W=1289:2,S
./mmccarn/Maildir/.Sent Items/cur/1527350162.M171903P6617.office,S=1628,W=1679:2,S
./mmccarn/Maildir/.Sent Items/cur/1527854968.M733872P11508.office,S=718,W=743:2,S
./mmccarn/Maildir/.sent-mail/dovecot.index.cache
./mmccarn/Maildir/.Sent Messages/dovecot.index.cache
./rmccarn/Maildir/.Sent
./rmccarn/Maildir/.Sent/dovecot.index.cache
./rmccarn/Maildir/.Sent Messages
./rmccarn/Maildir/.Sent Messages/dovecot-uidlist
./rmccarn/Maildir/.Sent Messages/dovecot.index.log
./rmccarn/Maildir/.Sent Messages/dovecot.index.cache
There is also a setting in Outlook for "save replies in same folder as message", which can scatter the sent items throughout a user's email folders.
Here's a command that should find "sent" items in any folder for a specific user
USER=mmccarn
cd /home/e-smith/files/users/$USER
find . -type f -ctime -1 -exec grep -H ^From\:\ .*$USER "{}" \;
* USER=mmccarn: run this command for the "mmccarn" user account
* -type f: include only files in the output
* -ctime -1: include only items created in the last 1 day
* -exec: run the specified command, replacing "{}" with the result from "find"
* grep -H: include the filename in the output from grep
* ^From\:\ .*$USER: find lines that begin with "From: ", and also include the username specified
./Maildir/.Sent Items/cur/1527707147.M277894P22460.office,S=39516,W=40289:2,S:From: "Michael J McCarn" <mmccarn@mmsionline.us>
./Maildir/.Sent Items/cur/1527352381.M370254P8981.office,S=8841,W=8993:2,S:From: "Michael J McCarn" <mmccarn@mmsionline.us>
./Maildir/.Sent Items/cur/1527945032.M147900P7953.office,S=1253,W=1289:2,S:From: "Michael J McCarn" <mmccarn@mmsionline.us>
./Maildir/.Sent Items/cur/1527350162.M171903P6617.office,S=1628,W=1679:2,S:From: "Michael J McCarn" <mmccarn@mmsionline.us>
./Maildir/.Sent Items/cur/1527854968.M733872P11508.office,S=718,W=743:2,S:From: "Michael J McCarn" <mmccarn@mmsionline.us>
./Maildir/cur/1527855192.M632509P11827.office,S=8686,W=8837:2,:From: M McC <mmccarn@mmsionline.us>
The last one looks odd, but I can review it using "less", and surrounding the message name with single quotes (it's an email test that matches on "^From: .*mmccarn" in the body of the email)
less './Maildir/cur/1527855192.M632509P11827.office,S=8686,W=8837:2,'