WS:Compress Out is a member of Websetters family of Microsoft Office Add-Ins. This Add-In extends the functionality of Microsoft Outlook 2000, 2002 and 2003. Every time you send an email that contains attachments, WS:Compress Out will automatically compress the attachment and resave in the mail item. This reduces the amount of storage used by you in your Outlook storage, reduces the time online and network bandwidth used, reduces the amount of storage used by your recipients - all saving you money.

http://www.websetters.co.uk/WSAddIns/Compress%20Out/index.htm