If you do get attachments regularly, like digital camera pictures, music, funny pdf or Powerpoint presentations or files like that you know the cause for the huge size of your mail folder. It slows down the application as well and it is a good idea to either delete or remove the attachments from the mails by saving them to a directory on the hard drive.

The Outlook Attachment Remover Add-in (via Shellcity) adds the Attachment Remover button to Microsoft Outlook which becomes active after selecting a folder or message.

It removes (detaches) the attachments from the selected mails in Outlook and replaces them with a link to their location on the hard drive. Some alternatives are to keep the attachments or to add a text reference instead of a link to the mail message when removing the attachment.

Two additional filters are available. The first specifies a minimum file size and the second file extensions that will be processed. If you want to detach all document types you use the format .doc;.xls;.pdf;.pps;.

Subfolders of a selected mail folder can be processed and the folder structure can be retained on the hard drive. I was not able to find information about the supported Outlook editions on the website.