What you need to know about spam filters

Email systems are widely used for business communication and collaboration. The problem is that they are often flooded with junk mail, otherwise known as spam. In fact, about 85% of the global daily email traffic is spam — that’s 122.3 billion messages per day!

Spam is commonly just a nuisance, mostly containing harmless ads and promotions. In 2020, because of the pandemic, a lot of junk mail mentioned products related to diagnosing and treating COVID-19.

However, spam can also be a gateway for malware, identity theft, and phishing attacks that can harm your company. To protect your business, your email system must have strong security measures in place, starting with spam filters.

Related reading: Why are emails still the number one target for cyberattacks?

What is a spam filter?

Spam filters are programs that assess incoming email to determine whether it should reach your inbox. Messages that these filters flag as unsolicited, unwanted, or dangerous are sent to the spam folder or blocked completely. This filtering process secures your inbox from cyberthreats while also ensuring that spam doesn’t bury the emails that you do want to receive.

How do spam filters work?

There are many types of spam filters, each using a different set of criteria to evaluate emails.

1. General blacklist filter

A general blacklist filter blocks emails that are from lists of IP addresses of known spammers collated by internet service and email providers and server administrators from user reports. Examples of commonly used blacklists are URIBL, SpamCop, and Spamhaus. These blacklists are updated regularly to include newly created email addresses by spammers.

2. Header filter

All emails have headers that contains the following details:

  • Date and time stamps
  • Security signatures
  • IP address of all the servers that the email went through
  • Other information that reveals where the mail came from

A header filter looks at the aforementioned information to detect anything suspicious, such as spoofed email addresses that are meant to trick the recipient (e.g., g00gle.com instead of google.com).

3. Rule-based filter

A rule-based filter assesses emails based on the conditions that you or your administrators set. For example, you may opt to redirect all emails from certain senders or those containing specific words to the spam folder.

4. Content filter

Just as its name suggests, a content filter analyzes the information in the email’s header and body to determine whether the message is spam. This type of filter is effective because it takes advantage of the tendency of spam messages to have predictable content. This tendency is due to the fact that all spam emails typically have the same basic objectives, such as:

  • To offer deals
  • To promote explicit material
  • To tap into people’s emotions and desires

Types of content that trigger the filter include:

  • Repetition of words commonly used in spam (e.g., “dear friend,” “limited time,” “discount,” “special offer,” “toll-free,” and “risk-free”)
  • Sexually explicit language
  • An image-heavy email body with very little text
  • Executable attachments (e.g., .exe, .js, .vbs files)
  • Links to blacklisted websites

Bulk commercial emails that do not contain a valid physical business address and a clear unsubscribe method are also flagged as spam.

5. Bayesian filter

Unlike other spam filters that are based on static rules, a Bayesian filter learns from your spam preferences and adjusts to them. When you flag an email as spam, the filter analyzes that message’s characteristics and then sets up rules accordingly. It then filters out incoming emails that have similar features.

You won’t have to worry about email-based threats ever again when you partner with SpectrumWise. Our email/spam protection service also provides spam filtering and utilizes first-class firewalls, automated quarantines, anti-phishing and sent-message testing. Learn more about this service by scheduling your FREE IT consultation.


Contact Us

"*" indicates required fields

This field is for validation purposes and should be left unchanged.