An .ost file is an offline storage file where you CAN (but don't have to)
store messages offline when working with an Exchange Server. I don't use
Exchange, hence, I have no .ost file(s).
Note that IMAP is similar in some ways to Exchange, but it is not the same.
I have two .pst files currently in use. One is where POP delivery occurs (if
I have POP accounts) and also where local item storage occurs.
The second is the structure used for IMAP. Mail is not stored locally (i.e.,
on my computer) in this second .pst file.
When I receive an email on the IMAP server, it shows up in my IMAP .pst
file. If I want to be able to see that message offline, I would need to copy
it to a local folder. When I'm disconnected from the internet, nothing shows
up in my IMAP .pst file.
It is entirely possible to use IMAP and keep email exclusively on the
server, with minimal local overhead in terms of disk space used.
It's also possible to use POP and IMAP in parallel--this can be useful if
you retrieve email using multiple computers (e.g., a laptop and a desktop),
and want to use IMAP access to manage what's on the server, rather than as a
way to read email.
But, this has nothing to so with Word, so I'm not sure why it's here. In any
case, for more detailed information about these intriguing topics, you might
try one of the Outlook, Windows Mail, or Exchange newsgroups.
--
Herb Tyson MS MVP
Author of the Word 2007 Bible
Blog:
http://word2007bible.herbtyson.com
Web:
http://www.herbtyson.com