Contents
- What is a spam filter?
- Why are spam filters necessary?
- How do spam filters work?
- How to avoid being marked as spam
What is a spam filter?
A spam filter is software designed to analyze and sort emails. The main task of the filter is to determine the relevance of a specific email to the user. Depending on the analysis result, the email can be sent either to the "Inbox" or to the "Spam" folder. In some cases, the spam filter may immediately block and delete unwanted messages.
At the first stage, the Internet Service Provider (ISP) filters out some spam messages by deleting emails coming from IP addresses listed on blacklists. Then, email services like Mail.ru, Yandex, and Google use their own spam filters to protect users from unwanted content. If a company sends emails through its own mail server, it can use corporate spam filters for additional protection of its commercial networks and to block advertising emails directed at employees.
Finally, each email is checked by individual filters that recipients configure in their mailbox settings or client applications. These user settings apply only to the specific account, allowing each user to individually control their electronic communications.
Why are spam filters necessary?
Spam filters play an important role in protecting users from potentially dangerous emails that may contain fraudulent links or malicious attachments. These filters help avoid contact with unscrupulous advertising and other unwanted messages. Without spam filters, users would be at risk of infecting their computers, losing personal data, and incurring financial losses.
According to Kaspersky Lab, over 48% of all emails in the Russian internet space consist of spam messages. This highlights the need for effective filtering mechanisms to protect users from unwanted content and ensure their safety online.
How do spam filters work?
Modern spam filters use various methods to evaluate and verify emails. The main methods include:
- IP address and domain reputation analysis: Filters refer to blacklists of IP addresses and domains known as DNS Block Lists. If the sender is on such a list, their message is blocked or marked as spam.
- Authentication protocol checks: The authenticity of the sender is confirmed using authentication methods like DKIM, SPF, and DMARC. Emails that fail authentication are classified as spam.
- Formal characteristic filtering: Filters analyze characteristics such as the absence of a sender, the number of recipients, and the presence of attachments.
- Header checks: Spam filters analyze the headers of emails to determine their origin and authenticity.
- Bayesian filtering by words: This method uses probabilistic classifications to analyze the content of emails and identify spam words.
- User engagement analysis: User feedback helps filters learn; if a recipient deletes an email without reading it, this can negatively impact the sender's reputation.
- Template-based filtering: Filters create templates based on previously recognized spam and compare them with new messages.
How to avoid being marked as spam
To ensure your emails do not end up in the "Spam" folder, follow these recommendations:
- Maintain sender reputation: Set up authentication for each domain from which you send emails.
- Warm up the domain and IP address: Start with small volumes of mailings from new domains, gradually increasing them.
- Use different email addresses: Separate senders by task types and create distinct email addresses for different types of mailings.
- Monitor reputation: Check if your IP address is on any blacklists.
- Consider the value of your mailing: Ensure your emails are relevant and useful to subscribers.
- Avoid spammy words: Do not use words and phrases commonly found in spam messages.
- Format emails correctly: Do not hide the unsubscribe link, pay attention to text formatting, and avoid attachments.