You might have had some archiving done to another PST
file. Check for another PST, maybe archive.pst under your
personal folders. Do a search on it. Once, if you find
it, add the archive.pst file as another mail box on your
Outlook and check and see if the missing emails are in
there.
Sounds like an archive issue though, it may have auto
archived on you somewhere down the line, and you have to
find the archive.pst files now.
Also do a search on *.pst on your entire system and
see what mailbox files you have out there. Hope this
helps....
