Archiving email can be a challenge. Most email either resides within a program on your computer or in a server on the Internet, depending on which email system you use.
Either way you have to find where your email resides, download it -- if you can -- and make a backup copy.
Email resides either:
1. Locally on your computer, where you open a program to access it, or
2. Remotely on your email host’s website, where you open a browser and navigate to a website to access it or configure an email client to access it