Cold Mailing Glossary letter s

SPAM filters

Spam filters prevent unwanted and unsolicited emails from entering or exiting our mailboxes.


Inbound filters protect you from unwanted messages landing in your inbox.


Outbound filters prevent spammers from distributing spam.


These filters are provided by the Internet Service Provider (ISP) to protect both ends of the email spectrum. Spam filters can operate within the software of your email client or be hosted on computer or cloud servers.

How do spam filters work?

All sorts of predefined rules, called algorithms, check your incoming and outgoing emails. They make thousands of checks to determine the quality and intended use of the message. All of these checks assign a score to the email in question. When an email passes a pre-determined score, it’s flagged as spam and blocked from reaching its destination.

Types of spam filter

Content filters check the body and title of your email for words consistent with spam use.


Header filters look into the header of the email source code for suspicious information—usually spammer email addresses.


Blacklist filters cross-reference suspicious IP addresses and domains for those that have been assigned an untrustworthy reputation. There is an abundance of blacklists on the Internet, many of which work with filters providing protection from recognized offenders.


Rules-based filters are customized rules that exclude emails from specific senders, or emails containing specific words in the subject line or the message body from being delivered.

Why are spam filters so important?

Any organization without an adequate level of spam filtering leaves itself wide open to attacks from phishing, virus infiltration, and malicious content. To protect your business and your customers from dangerous attacks, spam filters are your first line of defense.


They also prevent servers from becoming overloaded with unwanted and unsafe emails. Some spam messages contain software designed to turn your servers into spam servers themselves.

Are spam filters really necessary?

Absolutely! At a guess, around 70% of all email around the world is spam.


Why so many? Because it’s a big business, that’s why. The tricks spammers use to get what they want or need are more sophisticated and smarter than ever. Your spam filters are providing an incredibly valuable service, keeping your accounts clean, you in businesses and preventing you from unnecessary downtime, hacks, theft, and more.