Getting blacklisted can bring your email campaign to a screeching halt. After all, email, the most cost effective digital marketing channel is only truly impactful if your content reaches the inbox. Many marketers do not actively monitor blacklists and may not be privy the damage incurred to their marketing endeavors. ISPs and mailbox providers reference a variety of blacklisting services. If a sending IP is blacklisted it will be refused by all destination mail servers that reference the blacklist. This is a protection method against known spammers. Depending on the footprint or reputation of the blacklist service, a listing can be a slight inconvenience or a critical failure that renders a marketing campaign inoperable.