pst and dbx files

[Fennis]

Hello

I was wondering if you could help me. I am still trying
to understand something about pst and dbx files. I want
to know whether essentially pst files and dbx files are
the same. They obviously are not exactly the same, but
whether their structure is the same. I have been
speaking to different people, and what they tell me is
contradictory!

Do pst and dbx files work in the same way, such that when
you delete an email, you are not actually deleting the
email, but you are rather deleting the link that shows
where in the file the data is held,has now been deleted.
Which is very similar to a FAT system, and you delete a
file from a computer, you are not deleting the file
itself, but the reference to where the file is located. I
believe this is how a PST file works. Am I right in
saying this is how a dbx file works? I thought so, until
somebody told me that the pst and dbx files are totally
different file structure.

If you are able to clarify what I have said, and how
exactly the dbx file differs to the pst file, if it does
at all.

Many thanks

 

[Brian Tillman]

I was wondering if you could help me. I am still trying
to understand something about pst and dbx files. I want
to know whether essentially pst files and dbx files are
the same. They obviously are not exactly the same, but
whether their structure is the same. I have been
speaking to different people, and what they tell me is
contradictory!

PST (Personal Folder) files are the data store used by Outlook, a part of
the Microsoft Office suite of programs. DBX files are the data store used
by Outlook Express, part of Internet Explorer and Windows. They do not have
the same structure at all.

Do pst and dbx files work in the same way, such that when
you delete an email, you are not actually deleting the
email, but you are rather deleting the link that shows
where in the file the data is held,has now been deleted.

For PSTs, my guess is that a pointer to the message is modified to change
the "containing folder" field from the original folder to "Deleted Items".
When the Deleted Items folder is emptied, the message pointer is deleted,
with the data representing the original message staying in the PST. The
message data gets physically deleted (or overwritten) when the PST is
compacted or a new message overwrites the old data. For DBX files, I
believe the message is physically moved from the original DBX to the Deleted
Items DBX, with the pointer to the message in the original folder being
deleted. The message data itself remains in the original folder and gets
overwritten by new messages or cleaned out by a "Clean Up Now".

If you are able to clarify what I have said, and how
exactly the dbx file differs to the pst file, if it does
at all.

It would be impossible to state _exactly_ how they differ, and only
Microsoft engineers know all the details, but why not get a hex editor and
look for yourself?

 

[Fennis]

I appreciate your detailed answer and think I understand
how you have explained what happens for the pst file.
However, I am not sure if I quite understand what happens
for the dbx file.

The information you posted in the newsgoup was this:

When you delete an email from the Inbox or another mail
folder, the message is physically moved from the original
DBX file to the Deleted Items DBX, with the pointer to
the message in the original folder being deleted. The
email data itself remains in the original folder and gets
overwritten by new messages or cleaned out by compacting
the folder'



I am not entirely sure I understand this. So if you
delete an email from the Inbox, the email is then moved
to the deletedItems.dbx file. Does the email also stay
in the Inbox.dbx file? It is unclear as above you
say, "physically moved from the original DBX" which would
mean that it has been deleted. But then later on you
say "The email data itself remains in the original folder
and gets overwritten...".



So my first question is does the original email stay in
the Inbox.dbx file?



Secondly, leaving the other question aside, when the
email gets deleted from the deletedItems.dbx, what
actaully occurs? I am still unsure about this.



Any help you can give in clearing up this matter would be
much appreciated.

 

[Brian Tillman]

I am not entirely sure I understand this. So if you
delete an email from the Inbox, the email is then moved
to the deletedItems.dbx file. Does the email also stay
in the Inbox.dbx file? It is unclear as above you
say, "physically moved from the original DBX" which would
mean that it has been deleted. But then later on you
say "The email data itself remains in the original folder
and gets overwritten...".


So my first question is does the original email stay in
the Inbox.dbx file?

Yes, but without any way to locate the message data. The pointer to it is
removed.

Secondly, leaving the other question aside, when the
email gets deleted from the deletedItems.dbx, what
actaully occurs? I am still unsure about this.

Of couse all I described is merely an educated guess, but I believe the same
thing happens in Deleted Items.dbx: the pointer to the message data is
cleared so that there is no way to access. I also didn't mention
previously, that likely there is a map that indicates what areas of the file
are being used and what areas are available. It would be reasonable to
assume that the location occupied by the deleted message's data is marked in
this map as available for use so that, when another message gets stored in
the file, the program can easily locate an area of the file that can hold
it. So, in many respects, maintenance of the DBX (and PST) files is handled
in a fashion similar to how the file system handles disk allocations.

By the way, my educated guess is based on well-accepted Computer Science
principles and the behavior of programs like DBXtract
(http://www.oehelp.com/DBXtract/Default.aspx).