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How Spam Filtering Works | Ways To Prevent Harmful Emails

Spam Filtering is a process where spam filters detect unsolicited, unwanted, and virus-infested email (called spam). Stopping them from getting into our general email inboxes.

As an example, Internet Service Providers (ISPs) use spam filters to make sure they aren’t distributing spam. Small- to medium-sized businesses (SMBs) also use spam filters to protect their employees and networks.

Here: Best Cheap Internet Providers in Kenya for home, office: Nairobi wifi, wireless services

In addition, during the Spam Filtering procedures, spam filters are applied to both inbound email (email entering the network) and outbound email (email leaving the network). And in that case, ISPs use both methods to protect their customers. Whereas, SMBs typically focus on inbound filters.

How does Spam Filters work?

In the first place, there are many spam filtering solutions available. Not forgetting, they can be hosted in the “cloud,” on computer servers, or integrated into email software such as Microsoft Outlook.

Spam filters use “heuristics” methods, which means that each email message is subjected to thousands of predefined rules (algorithms).

In general, each rule assigns a numerical score to the probability of the message being spam. And if the score passes a certain threshold the email is flagged as spam and blocked from going further.

Generally, there are two types of Spam Filtering process. Including,

  1. inbound spam filtering,
  2. outbound spam filtering, and
  3. SMTP relay service

What is Inbound Spam filtering?

Inbound email is an email that is sent TO your inbox. With this in mind, therefore, inbound spam filtering is the act of filtering an email that is sent to your inbox to ensure it is not spam.

When spam is attempted to be sent to your inbox, most of the time your email service provider will block it using an inbound spam filter.

Given that the number of spam emails sent worldwide every day far exceeds the number of legitimate emails sent. So, inbound spam filtering helps to keep our inboxes safe, secure and manageable.

Fundamentally, every spam filter is a classifier that attempts to accurately guess whether email recipients will consider a piece of email to be spam.

Here: How does inbound spam filtering work?

What is Outbound Spam filtering?

Service providers and enterprises need to pay attention to the spam exiting their network in the outbound direction. If left unchecked, outbound spam will cause the service provider’s network to be blocked by the rest of the internet — effectively stopping legitimate email traffic for all network customers.

This happens as part of the global effort to stop inbound spam from harming users. Sophisticated reputation systems have been established to track the amount of spam coming from each IP address on the internet.

These systems block IP addresses that send too much spam, and rate limits those with questionable sending practices, by blacklisting them. Outbound spam filtering addresses the challenge of IP blacklisting that occurs when your network is blocked because spammers have managed to infiltrate it and use it to send spam.

Here: How does outbound spam filtering work?

What is an SMTP relay service?

An SMTP relay service is a hosted mail server that delivers email on behalf of clients. Companies that struggle with email delivery issues can use an SMTP relay service to get an email delivered more reliably.

An SMTP relay service can also help secure the network and proactively identify compromised accounts and scripts.

Jump to:

  1. Why Outsource Email Delivery? 
  2. Spam is the Only Constant on the Internet 
  3. How SMTP Relay Services Work 
  4. The MailChannels Difference
  5. Tools That Give You Real Network Insight
  6. Take the Mystery out of Deliverability

Is Spam Filtering necessary?

In today’s world, spam filtering is a must to protect your business. Spam is not going away. For instance, it is estimated that 70 percent of all email sent globally is spam, and the volume of spam continues to grow because spam remains a lucrative business.

Spammers get ever more sophisticated and creative in their tactics to get their messages into your inboxes and wreak their havoc. Therefore, spam filtering solutions must continually be updated to address this evolving threat.

There are different types of spam filters for different criteria:

  • Content filters – parse the content of messages, scanning for words that are commonly used in spam emails.
  • Header filters – examine the email header source to look for suspicious information (such as spammer email addresses).
  • Blacklist filters – stop emails that come from a blacklist of suspicious IP addresses. Some filters go further and check the IP reputation of the IP address.
  • Rules-based filters – apply customized rules designed by the organization to exclude emails from specific senders, or emails containing specific words in their subject line or body.

You can also run your message through certain tools, such as Mail Tester to test the ‘spammyness’ of an email.

No single method is a complete solution to the spam problem, and there are always trade-offs (which the heuristics try to weigh) between rejecting legitimate email vs. letting spam slip through.

Why is Spam Filtering important?

A spam filtering solution cannot be 100 percent effective. However, a business email system without spam filtering is highly vulnerable, if not unusable. It is important to stop as much spam as you can, to protect your network from the many possible risks. Such as viruses, phishing attacks, compromised web links, and other malicious content.

By preventing spam email from reaching your employees’ mailboxes, spam filters give an additional layer of protection to your users, your network, and your business. At the very least, spam email is a nuisance that will clog up your employees’ inboxes and overload your servers.

Spam is also dangerous as it is the entry point for serious attacks that could damage your reputation. In addition, it can also damage your computers, your computer network, and even your bottom line. Of course, Yes! You need a spam filter solution as the key first line of defense.

What is Phishing?

To enumerate, Phishing is a cybercrime in which a target or targets are contacted by email, telephone or text message by someone posing as a legitimate institution. Especially, to lure individuals into providing sensitive data. Such as personally identifiable information, banking, and credit card details, and passwords.

In fact, Old School Security Awareness Training doesn’t hack it anymore. Today, your employees are frequently exposed to sophisticated phishing and ransomware attacks. Other than email and website phishing, there’s also ‘vishing’ (Voice Phishing), ‘smishing’ (SMS Phishing) and several other phishing techniques Cybercriminals are constantly coming up with.

Here: How does Phishing Attacks occur?

How can Spam Filtering help you?

On the contrary, your IT Team is small, usually overloaded and unable to handle a large number of users who are the source of all kinds of problems. Including, malware infections through email phishing. Therefore, you need a security awareness training program that can be deployed in minutes. Protecting your network and actually saving you a lot of time.

When you decide to invest or upgrade your spam filter solution, know that there are countless spam filter programs out there. And also, it will take time to figure out which one works best for your business.

Here are a few key things to look for:

  • At a minimum, the solution you choose must block spam. This might sound like a given, but not all spam filter software is up to the job. Or even, doesn’t keep up to date with the evolving world of spam attacks.
  • The solution you choose must provide the security you need for your network, but not stop the legitimate emails your employees need to conduct their business.
  • Administrators must have the ability to edit and create rules over and above predefined rule settings. So that in the end, the solution meets your organizational needs. However, this customization should be easy, even for unsophisticated computer users.


As an example, a bank will not ask for personal information via email or suspend your account if you do not update your personal details within a certain period of time.

On the other hand, most banks and financial institutions also usually provide an account number. Or even, other personal details within the email, which ensures it’s coming from a reliable source.

In reality, phishing emails usually appear to come from a well-known organization and ask for your personal information. Such as credit card number, social security number, account number or password.

Resourceful References;

I hope you have gathered enough information in regards to the above-revised guide about Spam Filtering. But, if you have additional information, contributions or even suggestions, please Contact Us.

You can also share some or more of your thoughts in the comments box below this post. Below are more additional and related to the topic links.

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  3. Computer Hacking » User-based Safety Tips
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