Flamemail

Such knee-jerk reactions will usually lead to a volume of unwanted, unnecessary and uncomfortable flamemail directed at you and occasionally every company e-mail address that the Internet rovers can find.

Source: wiktionary

Flamemails may be used as a shield for the manager who lacks the skills of face-to-face communication or for someone who would rather avoid any type of direct confrontation with others.

Source: wiktionary

A commercial and retail bank employee sends a “flamemail”. The defamatory email details experiences with an identified customer. It is circulated internally, but someone leaks it.

Source: wiktionary