Mac Mail won't send mail

I can't send mail on my iMac. I can from my Mac Mini and my notebook. I've tried a number of things which I list below:

Disc utility/repair - nothing
Opened Mail in a different user and it works
Removed plist files
Reinstalled Mail

any other suggestions?

can you receive mail?

are the mini/notebook running the same OS?

Yes, all the other macs are on the same operating system. I could receive mail when this first started. I only could not send. But now after my troubleshooting, I can't receive either.

i would completely delete the account and then have one of your machines that works right next to you to be sure all the settings are the same when you set it up. if you were getting mail it was working and i would bet you had something wrong on your smtp settings. be sure to check the outgoing port settings on your account. some ISP's require you to use theirs and some will let you use your email providers it varies.

hope that made sense

NOTE: Nothing to do with Desktop Hardware. Moving to Software forum.

I've done all of that! I have even created a new user and it works like a charm. So something is wrong with my main user.