When in the workplace or school
and there is an email system.
A fellow co-worker or student the system by sending emails to everyone who is on the email system.
This often leads to abuse of the email system and can result in having your email inbox
spammed by a Mass-emailer.
This can also be irritating because often mass-emailer's will stop stop at just one mass-email, but go on to send more and more and clog up your inbox so that it is full of useless shit.