Erase Mail settings and import mailboxes

I'm having trouble with Apple Mail 3.5 and think that it's isolated to my personal settings within the home dir. Often, when I receive attachments on my IMAP email account, they come through as plain text rather than an attachment. The same message w/ attachment is received properly on my laptop, so I know it's isolated to my desktop computer. Since my home directory is network based, I tried logging into another desktop on the network and experienced the same issue. I'd like to wipe all my mail settings and set-up the accounts fresh. The IMAP messages are not a problem, but I need to know how to properly back-up and import my old messages that are stored on the hard drive?
I don't know what else to do to solve the problem? I've tried deleting all cache and repairing permissions, etc. It must be something with the mail preferences or settings!?!?!?
Thanks in advance


Close Mail, move the file from the folder <home>/Library/Preferences to the Desktop and re-start Mail. It will start up as if it has never been configured before and ask you to create your primary email account. If you have more than one email account you can add them via Mail Preferences after Mail loads.
Your old messages (the ones under "ON MY MAC") are stored in the folder <home>/Library/Mail/Mailboxes and should remain unaffected but if you are a bit nervous about losing any of those messages then drag the folder <home>/Library/Mail to your Desktop so that you can import the messages after you have set up your accounts as per above.