Recall that spam is unsolicited commercial e-mail. While many consider spam a nuisance rather than an attack, it is emerging as a vector for some attacks. 

Explain that mail bombing is another form of e-mail attack that is also a denial of service (DoS), in which an attacker routes large quantities of e-mail to the target. 

Comment that phishing attacks may occur via e-mail, but they are aligned with social engineering designed to trick users to perform an action then making them a target of a larger DoS e-mail attack.