As the .PST file is used to store the private folder of a user it cannot get
rebuilt by the Exchange server. The .OST file is a local copy of the
calendar-entries; as they are also held at the Exchange server, this file
can get rebuilt.

We have the same problem with the .PST files as they are growing with nearly
unlimited speed. They all reside on a userhome server and ADSM has to use
more than 75% of its time just to transfer .PST files. Unfortunately they
get touched by Outlook even when there aren't any changes...

When doing the backup during nighttime I get most of the files, only a few
get skipped due to users not having logged out properly before going home. I
have no proof of it but I think that Outlook still running does not
necessarily lock the .PST. I think there are much more users that do not log
out than there are skipped .PSTs every night.

Regards,
Michael