The snipping tool saves as an image not text. You lose any links and attachments.
It depends on whether you are using an email program on your computer (like Outlook) or you are using an ISP email service like AOL or Gmail. Some of the ISP providers allow you to archive and download the files and some don't have that function. And even if they do, you still need a program on your computer that can open the archive.
Printing to a PDF file is probably the easiest way to save email in a text format if you are using an ISP service. If using an email program on your computer you simply backup the email file to an external thumb drive or hard drive or a DVD periodically.