It depends on what you mean by “data file”. Are you talking about your local PST file or the Exchange mailbox database file? You did not say if this was an Exchange account. If it is, please tell us what version of Exchange. Reducing the size of the data file in Exchange would require an offline defrag of the database. Your version of Exchange would determine the steps to take, if these are Exchange accounts. And if these are Exchange accounts you can set a corporate wide deletion policy on the mailboxes, but again the version would determine the steps to take.Please provide more details. Thanks.