Store attachments in a central location - If you do receive attachments, it is a good idea to store shared documents in a central location such as a TeamRoom database or file directory on the network. It not only saves space in your mail but it also helps guard against potential loss if damage occurs to your machine.
If you need the email that the attachment came in, one suggestion is to
1 - detach the attachment
2 - edit the email, (Ctrl-E)
3 - enter the location of the attachment
4 - delete the attachment from the email
5 - save the mail message.
This way you have the relevant info to the attachment, without the attachment bulking up your mail file.