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SteveHigh (TechnicalUser)
15 Nov 07 7:42
Hello

I am writing to ask what the difference is between an OST file and a PST file in Outlook 2003.

As I understand it, Outlook stores everthing - inbox, calendar appointments, etc - in Outlook.pst. As I
understand it, this pst file is held on the local user's hard drive and not on any network server.

At the same time, Exchange server copies messages (messages only?) to an OST file on a user's hard drive (as opposed to the network server), so that they can be read offline.

What, then, is the purpose of the pst file when the user can see his messages in the ost file? Is it that the user can see ONLY email messages which have come through Exchange server, as opposed to, say, calendar or journal entries which are available in the pst file, and are the email messages which have come through Exchange server duplicated so that you can see the same message in the pst
file as in the ost file?

Many thanks for your help.

Steve




Helpful Member!  itpro34 (MIS)
15 Nov 07 19:26
The difference between an .ost file and a set of .pst files is that the .ost file starts as a mirror image of your folders on the Exchange Server, and works in conjunction with the Exchange Serve during synchronization. A set of .pst files, on the other hand, is simply a storage location on your hard disk or a server other than the Exchange Server.

When you work offline, you can add, delete, and modify the contents of an .ost file exactly as you would with a folder on a server. For example, you can change and move items in your offline Inbox, send messages that are placed in your offline Outbox, and read your offline public folders. In the meantime, information on the server is still processing. You continue to receive new messages in your mailbox while other users can add, delete, and change items in public folders. However, you are not be aware of these changes on the server until you connect to the network.

When you need to update the contents of the .ost file and its corresponding server folder so that they are identical, you synchronize the folders, and then continue to work offline. In Outlook 2002, this is done through Send/Receive Groups. Synchronization connects to the server through Dial-Up Networking, copy the changes made in each folder to the other folder, and then disconnect. An item that you delete from either the .ost file or the corresponding server folder is deleted from both after synchronization.
SteveHigh (TechnicalUser)
16 Nov 07 10:22
Hello itpro34

You have made it much clearer as to what the role of an .ost file is - thanks - but in the jobs I have had, if a user calls in a panic to say he can't see his inbox, etc we always needed to locate the pst file - not the ost file.

Yet if the pst file is 'simply a storage location on your hard disk', wouldn't it make more sense for users to concern themselves about their ost file, especially if it
works in synchrony with the server simply by pressing Send/Receive Groups?

Or am I completely confused!?

Best regards

Steve
58sniper (MIS)
16 Nov 07 18:06

Quote:

if a user calls in a panic to say he can't see his inbox, etc we always needed to locate the pst file - not the ost file.
That would be true if mail delivery was to a .pst file instead of the mailbox.

Quote:

Yet if the pst file is 'simply a storage location on your hard disk', wouldn't it make more sense for users to concern themselves about their ost file, especially if it
works in synchrony with the server simply by pressing Send/Receive Groups?
That depends on where email is being delivered. In an ideal situation with Exchange, there shouldn't be .pst files. And, if there are, they should be in the default location in the users' profile, and NEVER on a server.

Pat Richard
Microsoft Exchange MVP

SteveHigh (TechnicalUser)
19 Nov 07 7:03
OK, I think I am clearer: a PST file contains the details of calendar entries, appointments, messages, etc. This might explain why users have called me in a panic: they can't see that morning's appointments, etc. If this file 'goes missing', it can be located in the user's (Windows) profile alongside, usually, favourites, user settings, etc.

On the other hand, messages on the server are copied not to the PST file, but to the .ost file, and this allows the user to add, delete, and modify items in the Inbox while offline and line up messages to be sent when online.

How, then, do messages end up in the PST file? Or don’t they, unless as you say, mail delivery is to a .pst file instead of the mailbox? If mail delivery is to the inbox – and not a .pst file – do messages simply go to the inbox and a copy placed in the .ost file?

The reason I am a little fussy about understanding this is that I am studying for the MCDST certificate and have the Microsoft book here and that states that the default folder for messages is the PST file.

Many thanks.

Steve
58sniper (MIS)
19 Nov 07 19:23
Well, let me shed some light.

An .ost file is just a local copy of the Exchange mailbox. If mail is delivered to the mailbox (as opposed to a .pst), then the .ost would contain email, Contacts, tasks, calendar items, etc. An .ost file is only used when Outlook is in cached mode (recommended).

A .pst file, on the other hand, may or may not exist. The can be manually created by the user, or they may be created as part of Outlook's Archive feature. They can contain just about any type of item. They are generally frowned upon if you have Exchange, as Exchange is a much better storage solution for mail items.

Pat Richard
Microsoft Exchange MVP

SteveHigh (TechnicalUser)
20 Nov 07 7:26
Seems as if pst files are somewhat superfluous. Thanks for your help and pateince.

Steve
RFBaker (TechnicalUser)
22 Nov 07 11:54
In and exchange enviroment most users use a PST as secondary storage archiving old Emails to the PST to stop their mailbox going over its size limit.

Richard Baker

58sniper (MIS)
22 Nov 07 13:09
But that's a poor excuse. There are dozens of reasons not to use .pst files. You gain nothing by using them.

Pat Richard
Microsoft Exchange MVP

Gavona (TechnicalUser)
22 Nov 07 15:07

Quote:

most users use a PST as secondary storage archiving old Emails to the PST to stop their mailbox going over its size limit.

Quote:

But that's a poor excuse.
As a user with an email box with a size limit what are you suggesting I do with emails that I want to keep - print them out, save individually in some other format or archive to a PST file where I can search them, use categories to group those with similar characteristics etc.
Whatever solution you suggest am I in danger of spending far more time managing my emails than is worthwhile given the relative cost of my time and of storage?

Gavin

58sniper (MIS)
22 Nov 07 20:56
Management of emails is the user's responsibility. I have a client with 180,000+ users. All have a 35MB limit, and cannot create .pst files. Users learn real quick about how to manage email.

I've seen companies face large legal fees because of .pst files. It's nearly impossible to do discover on them. You can't virus scan them. They don't automatically compact. There are size limitations. You shouldn't put them on network servers or mapped drives. They corrupt easily. Migration to new hardware is more complicated. The list goes on and on.

Pat Richard
Microsoft Exchange MVP

Gavona (TechnicalUser)
23 Nov 07 4:21

Quote:

Management of emails is the user's responsibility.
I do not disagree but I do think it is IT's responsibility to give us the tools and instruction to do that effectively and efficiently.  Your bald statement is not enough.

I recognise and accept the points in your second paragraph.  To me the long term solution is allow bigger OSTs and / or implement a corporate archiving solution (whatever that means) that does not have those downsides.

In the meantime how can I efficiently, electronically manage an archive of emails given an environment such as that in your organisation - no PST and a 35mb OST file limit?

Thanks,

Gavin

58sniper (MIS)
23 Nov 07 12:28
Saving emails because they have an attachment is just a bad idea. Detach that file to the file system, and whack the message. A user can have quite a few emails if there aren't any attachments.

Implementing auto emptying of the deleted items upon closing of Outlook will help as well.

Pat Richard
Microsoft Exchange MVP

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