<p>MFCMAPI, the well-respected reveal-behind-the-scenes utility for Exchange, has a little brother called MRMAPI, which is now capable of reporting the bloat that exists within OST and PST files.</p><p>MRMAPI has an interesting history. MAPI is full of tags that are used to describe the properties of items stored in Exchange mailboxes. Originally we just stored messages but now all manner of different items are stored in mailboxes including things like administrative audit entries. And as the variety of stored items expanded, so did the set of MAPI property tags. No human being is capable of remembering the full set, especially as tags use perfectly obvious and highly memorable names like PidTagAddressBookContainer (or 0xFFFD0003 as the tag is known to MAPI).</p><p>MRMAPI first appeared as MrTag, a utility to report all known MAPI tags. It has been expanded over time and is a great way to find out what tags exist so that developers reference the right tag or don't end up creating a new tag when one already exists.</p><p>I suspect that few outside the select group of programmers who care about MAPI would give MRMAPI any time if it just existed to tell you what MAPI property tags exist. But it is interesting when it provides an insight into the white (unused) space that exists in PST and OST files.</p><p><a href="http://windowsitpro.com/blog/mrmapi-little-brother-mfcmapi">Keep reading...</a></p>