Password for a Mail folder

I know how to use Disk utility to set up a password protected disk image for storing files. How can I do the same for a file folder in Mail? I want other to have access to my inbox while keeping emails I place in another folder private.

I don't know of any way to do what you want to do. Why on earth would anyone be using your email account other than you?

The "solution" is to give "other" their own user account and email address. People -- even spouses -- should not share an email account, it just creates problems.