[Reference:, https://books.google.com.pk/books?id=QzndBAAAQBAJ&pg=PA469&lpg=PA469&dq=symantec, +characteristics+for+an+email+to+be+considered+Spam+unsolicited, +malicious&source=bl&ots=I_T3VTUt18&sig=ACfU3U2lvi_cJl3o9tiMTnm_vZUf2sj8Fg&hl=en&sa=X&ved=2ah UKEwj34oGA1dHoAhWrBWMBHYVLB8cQ6AEwCXoECA0QJg#v=onepage&q=symantec%20characteristics, %20for%20an%20email%20to%20be%20considered%20Spam%20unsolicited%20malicious&f=false, ]