Thread Compressor for Microsoft Outlook
Thread Compressor is a nice add-in for Microsoft Outlook, developed by Ewan Dalton, that can really help you saving storage space.
“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.
Let me say that again: Thread Compressor, as it is configured by default, WILL DELETE DATA FROM YOUR INBOX.
If you choose to download it and use it from here, you do it with the author's blessing, but it's completely at your own risk and Microsoft cannot be held responsible for what it does.”