The practical limit is your own choice. The technical limit by default is
20GB but can be increased via the registry.
See http://www.msoutlook.info/question/99
I would recommend against using pst-files in a managed environment and use a
server-side archiving solution instead.

Signature
Robert Sparnaaij [MVP-Outlook]
Coauthor, Configuring Microsoft Outlook 2003
http://www.howto-outlook.com/
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http://www.msoutlook.info/
Real World Questions, Real World Answers
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> Have client with Exchange Mailbox who is archiving important messages into
> their Personal Folders Inbox with an extensive sub-directory structure.
[quoted text clipped - 5 lines]
> of the pst file Outlook 2003? Overall I would be glad of any advice as to
> what can be done to archive large amounts of Email data?