This would not block URLs or UNCs in general, but rather links to a shared folder or printer that might be attached via Outlook or other Windows applications.
Perhaps the most appropriate place to filter PIF files is at the gateway. This way you would block unsolicited PIF files but would still be able to attach them for internal e-mail. PIFs and other links do help keep down the size of e-mail items and are generally a better practice than full sized attachments.
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This was first published in July 2005