Mac mail program

I use 10.7.5 on a Imac G5 intel. Until recently I have used the Mail program and been quite happy. Suddenly the program is all screwed up , I still receive messages but the left side of the window shows the mailboxes I have created but has now added duplicates and additional mailboxes none of which can be deleted. As a result I am ready to find a new email program. I would appreciate any assistance or suggestions.

a. There is no such thing as an iMac G5 Intel. Given that you are running Lion, you must be using an Intel iMac.

b. Wouldn't it be better to solve the actual problem rather than just replace the email program, since the issue might also show up on your alternate email program as well?

We can help you troubleshoot the issue if you'll help us by telling us your email provider (or if you have more than one account, providers). If you know, specify whether your account is POP or IMAP. Chances are very high that the problem is being caused by modifications made on the server of the mail provider(s) by you or someone else. You cannot of course delete those server-side mailboxes from your mail program, which is why I think that switching mail programs isn't going to solve the issue.