Depends how you do email. I use a client, not a MS one, so I can just copy a single directory tree to a USB drive.
If you use web mail, like Gmail, where all your emails are stored on a server then they'll be safe.
I have noticed that MANY people have come to this forum using various MS email systems that have not converted nor run properly after the upgrade so I would back email up for sure. A friend of mine had some small problems with different versions of MS Office Outlook.