Introduction
Email bombing is a type of attack where the attacker uses automated bots to subscribe a victim’s email address to multiple lists per second, including forums and message boards, newsletters, retail mailing lists, and other everyday communications.
Procedure
Some of the emails contain keywords like 'unsubscribe' or similar. You can create a filter to put any received email containing that keyword in a separate folder. That is the only way to reduce the impact of such attacks.
How to create a mail filter to filter email for a specific subject