Any email account on your phone other than your "Microsoft Account" should have a "delete" option. If it's your Microsoft Account, you'll have to reset your phone to remove it.
I use my main email address from my cable provider as my "Microsoft Account ". The Microsoft Account doesn't sync mail from my cable provider. I have to set that up as a separate account using the POP or IMAP settings on order to sync the email from my cable provider.