neo said:
Note: The default way the .PST is created by Outlook is that it is a
compressed/encrypted file. As you permanently delete things (e.g.
shift + delete or delete and then empty Outlook's Deleted Items
folder), Outlook will reuse this white space.
My understanding of Outlook's database is that permanently deleted
items (i.e. not simply *moved* to the Deleted Items folder) simply have
their status changed to "Deleted" for their record(s). Outlook will
hide delete-marked items but they are still physically occupying space
inside the database file. Their byte space inside the database does
not get reused (as would, say, unallocated sectors on a hard disk that
were previously occupied by a file but to which the MSFT no longer
allocates to any file). Hiding a record is not the same as deleting it
nor can its space be reused. Not until you purge the database are the
delete-marked items physically removed from the database file (along
with some restructuring of record order and whitespace compression).
A soft delete merely *moves* the record into another folder (Deleted
Items). A hard (permanent) delete merely hides that record from being
shown by Outlook in its UI (it is still in the database). Bytes for
hidden delete-marked records does not get reused (it's dead but still
used space). Compacting the message store physically purges the
delete-marked records so their bytes are gone (and not available for
reuse).