If Apple's Mail program is asked to send a huge (possibly Gigabytes in size) attachment (sometimes after choosing a folder instead of a file in that folder) it can freeze up and make the computer really slow (as Mail uses more and more memory trying to process the attachment).
To recover from this situation (if you are using an Exchange or IMAP server) try these steps...
Quit from Mail Log in to webmail from a web browser and delete the message Delete it from the trash in webmail From the Finder, delete large files in: ~/Library/Mail/V2/emailaddress/Drafts.mbox Also large files in the invisible folder: ~/Library/Mail/V2/emailaddress/.OfflineCache In Mail: rebuild the Drafts mailbox
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