This tool originally was a long fabled internal Microsoft tool that finally has a somewhat proper "official" release to the web with plenty of warnings and caveats. It is an add-in for Outlook 2000/XP/2003/2007 which removes unnecessary emails, on the assumption that most people reply to mail and leave the original intact, so you could keep the last mail in each branch of a thread, and remove all the others. You would be surprised how often this happens!
It reduced the size of my Outlook mailbox by almost 1/5th tonight. Down to nearly 400MB from the original 500MB size.
Keep in mind - this program can and will delete e-mail content!
If you're in any doubt about this, then do not use this add-in.
You can download the add-in from
here and read more about it. The installation instructions might seem a little daunting, and it can act a little quirky on initial launch, but it is definitely worth running from time to time.
Original description rom the website with some history behind the plug-in:
Thread Compressor is an add-in to Microsoft Outlook, which removed unnecessary emails from a "thread" - reducing the amount of storage required (maybe keeping your mailbox within its size quota) and reducing the number of emails you need to read.
TC was developed inside Microsoft from 1999 onwards, and attracted a large following (up to 30,000 users) but has never (officially) been made available externally, due to the fact that it will delete data unless it is configured not to. I've decided to share it more widely now.
Originally spotted
here.