Our enviroment is currently running Exchange 2003 with Outlook 2007. A lot of users prefer to use a PST as their delivery location as space is not an issue. We do not give them much room on Exchange so they would have to Archive constantly. Increasing their mailbox size is not an option.
I've noticed that users that have an Exchange account deliver to a PST AND ALSO have an additional mailbox have an issue where certain emails download to their PST, but don't delete it from the Exchange server when completed. This causes the same email to continually download into their PST. The only way to stop it is to log onto OWA and manually delete the email.
There is no setting to "Keep on the Server for X amount of days" when you're set up as an Exchange account (it doesn't exist). SMTP mail is also not an option to resolve this issue.