Lost email

I have Macbook Pro running 10.6.7. I switched my email addresses recently. When I deleted the old accounts, my inbox and sent messages disappeared. I suspect I could find them in Terminal but I am not versed in command line. I don't want to do anything that would possibly delete these messages as many are very important. Any ideas?

When you deleted your old accounts, you should have received a warning from the Mail app telling you that all your email messages would be removed.

If you didn't make a backup by exporting those messages before you deleted the accounts, they're gone. It's like emptying the Trash.

Terminal

I was not prompted that I would be losing all my messages. The only ones that disappeared were the ones still in the INbox and the ones in the Sent box. All my other mailboxes where I file things are still there. When I looked in the user library, I found many that were there from a previous email address that I thought were long gone. These were in INboxes and Sent boxes. Just not the most recent ones.

That's correct. Anything you had in personal folders will not be removed but all else will. You may be able to access your account directly on the Web and just re-download what's missing. I sometimes have to do that with my GMail account.