Can I open email from an old iMac into a new client?

Joe has a 2009 iMac with a bunch of emails on it, dating back to 2003. He wants to know how to open them in another email program, along with the contacts as well? Leo says it varies according to the email program you use. Leo says that since Apple Mail exports to MBox, you can open that format into just about any other email client. You can even open them in a text editor to see what's in it. Apple Mail will import them easily, and Thunderbird should be able to as well. Leo also recommends using SuperDuper to back them up.