OneNote offers the ability to save emails simply by emailing me@onenote.com (more information can be found in Microsoft's "Email to OneNote" guide).

In order to use this feature, your primary email address in Connect (the address which appears when your name is searched in Connect and serves as your default “From” address) must exactly match your UPN (short for “User Principal Name” – the address which you use to log into Connect). If these addresses do not match, you will need to save emails manually when you wish to place them in OneNote.