MX records

This may sound like a silly question, but can messing with the MX records affect the actual website hosting itself?

Or are MX records purely related to email?

 

Changes to the MX record will not affect the site.

 

Can I user Smartermail as a backup MX record (value 20), and direct primary MX to my Exchange server?

 

You could, though not usually recommended because the email servers do not talk to each other, so if by any chance your Exchange server isn't available for an email and it goes to the Smartermail server, then you'll actually have to keep checking on both email boxes to check there's no mail.