Crazed email sending old messages over... and over

Question

Help. Mail is resending messages every time it is reopened. This is tiresome, and is causing confusion with my contacts, some of which are business related.
I've done a safeboot, utilities, and have resorted to using the mac mail on the website to that on my desktop, which is a significantly inferior option.
700 Power PC G4 Mac OS X (10.4.9)
700 Power PC G4   Mac OS X (10.4.9)  

Answer 1

There is a kind of index corruption that causes messages to randomly appear in a mailbox different from where they’re supposed to be. If that mailbox happens to be the Outbox, Mail thinks they’re waiting to be sent and dutifully proceeds to try to send them.
Verify/repair the startup disk (not just permissions), as described here:
The Repair functions of Disk Utility: what's it all about?
After having fixed all the filesystem issues, if any, and ensuring that there’s enough space available on the startup disk (a few GB, plus the space needed to make a backup copy of the Mail folder), try this:
1. Quit Mail if it’s running.
2. In the Finder, go to ~/Library/Mail/. Make a backup copy of this folder, just in case something goes wrong, e.g. by dragging it to the Desktop while holding the Option (Alt) key down. This is where all your mail is locally stored.
3. Locate Envelope Index and move it to the Trash. If you see any other “Envelope Index”-named file there, delete it as well.
4. Open Mail. It will tell you that your mail needs to be “imported”. Click Continue and Mail will proceed to re-create Envelope Index — Mail says it’s “importing”, but it just re-creates the index if the mailboxes are already in Mail 2.x format.
Note: For those not familiarized with the ~/ notation, it refers to the user’s home folder. That is, ~/Library is the Library folder within the user’s home folder, i.e. /Users/username/Library.