When you zap an account you unfortunately zap all the email associated with that account's inbox, sent mailbox, etc.
Depending on how old your backup is, the easiest will be to just copy the old (backed up) Mail folder and replace the one on your current hard drive. This will replace all your new settings and set you back to the day you backed up. I would then try and put in the new settings (replacing the old settings instead of making a new account)
Depending on how old your backup is, the easiest will be to just copy the old (backed up) Mail folder and replace the one on your current hard drive. This will replace all your new settings and set you back to the day you backed up. I would then try and put in the new settings (replacing the old settings instead of making a new account)