OUTLOOK EXPRESS 6 is sending multiples of same email

It has been happening over last 10 days or so that when I send an email, recipients report getting it anywhere from 2 to 43 times! And my messages I send out, no longer register into my SENT box. I have tried compacting folders, searching out my "outbox.dbx" and then deleting it, and doing a scan with SCANdbx, to no avail. I have Windows XP Pro, so wondering what else there could be that I could do to remedy this problem. I have also gone into START>RUN & typed in msimn / reg >OK and still doesn't help.
Not sure I want to uninstall & reinstall this program . . . I use my system for business & run two websites so with my luck, I'd LOSE all my info. Let me know if there is a definite fix if anyone out there can recommend one.

Thanks!

Is your mail account through your ISP ? if it is give them a call and see if the problem is on their end.

Try Thunderbird and see if the problem persist.

Try this:

Tools > Accounts. Highlight your mail account and hit properties.

On the Advanced tab make sure "Break apart messages larger than" is unchecked.

Click Apply.