AdGuard 部落格 How to block spam emails

How to block spam emails

2023年11月16日閱讀時間為 35 分鐘

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Currently, about half of the world's population has access to the Internet as well as at least one email address. And, of course, almost every email user knows what spam is. The next question that arises would be how do you stop unwanted emails, we will come to it later on, but let us delve into some history first.

Email as we know it was introduced in the early 1970s, and the first case of spam dates back to May 3, 1978. The first spam email was sent by Gary Thurrock to 393 ARPANET users (the predecessor of the modern Internet) and contained an advertisement for a presentation of new DEC computers. Therefore, it can be said that spam has been around as long as email has existed.

Spam represents more than just unsolicited advertising offers. Viruses, phishing emails and various other scam schemes can lurk among these messages. By clicking on a malicious link or opening a malicious attachment from such an email, we risk losing identifying information, falling victim of a phishing attack, identity theft, losing personal data, or even losing control of our computer.

Aside from that, spam puts a lot of strain on mail servers, slowing them down and degrading the quality of service. By constantly dealing with countless spam emails, email providers are forced to spend additional resources, which ultimately affects the cost of their services to us consumers.

The percentage of spam emails has varied considerably over time. At its peak, in the mid to late 2000s, spam accounted for up to 90% of all email sent worldwide.

However, with the advent of more advanced spam filters for users’ cybersecurity protection, as well as increased legislative measures against spammers in many countries, spam's share of total email volume has declined.

As of 2020–2021, spam accounted for about 50% of the total amount of email. It should be noted that most of it is successfully filtered by email services and does not reach users' mailboxes.

Ways to block spam emails

There are quite a few anti-spam techniques, and the more of them you use, the better protected your email is. Listed below is a selection of the most effective types:

Mail server-level filtering

Modern email services such as Gmail, Yahoo Mail and Outlook use sophisticated algorithms to automatically identify any suspicious email and place them in the spam folder. These algorithms analyze email content, sender behavior and other factors to identify spam, using machine learning techniques.

Allowed and blocked address lists

Users can manually add addresses to whitelists or blacklists. Emails from blacklisted addresses are automatically blocked or sent to the Spam folder.

Content-based filtering (Bayesian filter)

A Bayesian filter in terms of spam filters is a spam detection method based on probability theory. The filter learns from known examples of spam and normal emails by calculating the probability that an email containing a specific word is spam. When a new email is received, the filter estimates the probability based on the words it contains. If the probability exceeds a certain threshold, the email is classified as spam.

Behavioral analysis

Some systems monitor sender activity, such as the frequency or number of emails sent, in order to identify any unwanted spam.

Sender authentication

Thanks to technologies such as SPF, DKIM, and DMARC, you can verify that the sender's IP address corresponds to the domain from which the email is supposed to have been sent. These techniques help prevent phishing and other types of attack in versatile spam posing as harmless emails with unsubscribe links from nonexistent services and such.

Filter training

Users have the ability to adjust the actions of anti-spam filters, marking emails as spam or, conversely, as legitimate. Over time, this improves filtering accuracy.

Third-party anti-spam software

These are additional programs or plug-ins that can be installed to protect against spam. They usually combine several filtering methods and privacy settings, also providing advanced customization options.

Temporary email addresses

These are special addresses created for one-time use. These addresses are automatically deleted after a certain period of time.

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Alternate email addresses (aliases)

These are addresses that are created for entry on specific sites and redirect any messages that come to them to your primary email address. They protect it from being included in spam email address databases and can be deactivated at any time.

Each of these methods has advantages and disadvantages, and their effectiveness may depend on your particular situation. The best results are usually achieved by combining several methods to block spam email from your inbox.

How to block spam in popular email services

Most popular email services offer a variety of methods of how to block junk email. Let's consider the main ones.

Gmail

Auto-filtering

Gmail automatically recognizes most spam emails and moves them to your spam folder. Check this folder regularly in case of false positives.

Manual blocking

Open an unwanted email
Click the three dots next to the Reply button
Select Block [sender name]. Emails from this address will now be automatically sent to your Spam folder

Creating filters

Click the gear icon in the top right corner of Gmail and select All Settings
Click the Filters and Blocked Addresses tab
Click Create a new filter and set the filtering parameters
Click Create Filter and select the desired action, such as Delete

Marking an email as Not Spam

If you find an email from a trusted sender in your spam folder, open it and click Not Spam. This will improve Gmail's filtering efficiency just as well as the Report Spam tool.

Yahoo Mail

Fighting spam in Yahoo Mail is no more complicated than standard ways to block spam email in other services.

Auto-filtering

Yahoo Mail automatically filters many spam emails by sending them to your spam folder. Checking this folder regularly will help improve the filter's performance.

Block sender

Open an unwanted email
Click More in the top menu
Select Block Sender from the drop-down menu. Emails from this address will automatically go to your Spam folder

Creating filters

Click the gear icon in the upper right corner and go to Settings
Select Filters
Click Add and set the parameters for the new filter
Define an action for emails that match the filter conditions (e.g. Move to folder...)

Dealing with false positives

If a useful email ends up in your spam folder, open it and click Not Spam. This will correct the filtering and reduce the likelihood of future errors when your application works a bit too hard to block spam emails.

Outlook (or Hotmail)

Outlook offers effective tools to combat spam. Here's how you can minimize email spam in your inbox:

Auto-filtering

Outlook automatically detects any suspicious third-party email and moves them to your Junk Mail folder. Don't forget to check this folder for false positives.

Block sender

Open the Junk Mail
On the Home tab, click Junk Email, and then select Block Sender. All future emails from this sender will be moved to the Junk folder

Customize filtering settings

From the Home menu, select Junk Email and go to Junk Email Options
You can choose the level of filtering from No filtering to Low: Move the most obvious junk email to the Junk Email folder to Only obvious cases to Safe Lists

Adding addresses to Safe Lists or Blocked Senders

In the same Junk Email Options menu, add trusted addresses to Safe Lists and unwanted addresses to Blocked Senders

Marking emails as Not spam

If a useful email is in your Junk Mail folder, right-click and select Not Junk

ProtonMail

ProtonMail provides several tools to reduce the number of spam emails in your inbox. Among them:

Auto-filtering

ProtonMail automatically selects many known spam emails and sends them to the Spam folder. It is recommended that you check this folder occasionally for false positives.

Block sender

Open an unwanted email
Click More (shown as three vertical dots) and select Block

Creating filters

Select Settings at the top of the interface
In the Filters and Folders section, click Add New Filter
Set conditions for the filter and specify the desired action, for example, move emails to the Spam folder or delete them

Dealing with false positives

If a useful email was mistakenly placed in your spam folder, open it and click Move to inbox (not spam). This will help improve ProtonMail's filtering algorithms.

Top anti-spam programs for mail

SpamAssassin

SpamAssassin is an open source server-side spam filter designed for use on UNIX/Linux based systems. It is a flexible and modular solution embedded in the mail infrastructure and is designed to handle server-side mail traffic, most often used in combination with popular MTAs (Mail Transfer Agents) such as Sendmail, Postfix and Exim.

SpamAssassin applies a series of rules that check whether incoming messages have commonly known spam characteristics. The system uses a variety of techniques, including syntactic analysis of email text and headers, local and online reputation check lists (DNSBLs), and implements Bayesian filtering to adaptively learn from specific samples of spam and legitimate emails. SpamAssassin also supports many third-party plugins to extend its spam detection and filtering capabilities.

SpamAssassin requires configuration on the server on which it is deployed, which may include configuring MTA connections, configuring spam detection rules, and managing the mail queue. Depending on the configuration, SpamAssassin can delete suspicious messages, mark them in a special way, or move them to quarantine.

SpamAssassin is distributed under Apache License 2.0 and is available for free.

SpamAssassin has the advantages of being highly customizable and powerful for power users, but it can be difficult to install and configure for those without specialized IT knowledge.

MailWasher

MailWasher is a client-side email spam blocker app designed for Windows operating systems, with support for iOS and Android mobile platforms. It allows you to view and manage email before it is downloaded to your email client.

MailWasher connects directly to the user's mail servers via POP3 or IMAP, allowing users to view messages and decide which ones should be downloaded to the local computer and which ones should be deleted or marked as spam. Users can view the contents of emails without downloading them, reducing the risk of viruses and malware. The application filters spam using blacklists, whitelists and Bayesian scanning.

MailWasher requires installation on a local computer or mobile device. Once installed, the user must enter their email account details to get started. The program offers an intuitive interface that makes setup and use relatively easy for a wide range of users.

Price:
MailWasher offers a free version with basic features and a paid version that costs about $40 per year and provides additional features and support.

Benefits:

Possibility to preview messages without downloading them to the mail client
Multi-platform support with versions for desktop and mobile devices
Intuitive interface
Support for multiple email accounts
Ability to return accidentally deleted emails

Disadvantages:

Requires manual mail preview, which can be time consuming
Filtering options are limited in the free version
Not built directly into the mail server, requiring user action to manage spam

SpamBully

SpamBully is a client-based spam filtering application designed to integrate with Microsoft Outlook and Windows Mail on Windows operating systems. This solution is targeted at individual users and businesses that want to improve inbox filtering directly in their email client.

SpamBully integrates with email clients and analyzes incoming messages using a variety of methods to identify spam, including Bayesian filtering, automatic whitelisting and blacklisting, as well as spam phrase and sender quality analyzers. The program allows users to train the filter by marking messages as spam or non-spam, thereby improving the accuracy of further filtering, even with the most versatile spam messages.

SpamBully is installed as an add-on to an existing email client. Users need to follow the setup instructions so that the program can sync with their email account and start filtering messages. The application's user interface provides access to filtering settings and training options, making customization relatively easy for the end user.

Price:
SpamBully provides a 14-day trial version. A full license for the software costs $29.95 per year.

Benefits:

Direct integration with popular Windows email clients
Intuitive user filter training
Includes additional mail management tools such as a trusted sender list

Disadvantages:

Only available to Windows users and specific email clients
Requires license purchase after trial period expires
May not be suitable for inexperienced users who have difficulty understanding filtering settings

SPAMfighter

SPAMfighter is a spam filtering plug-in designed to integrate with Windows client email applications, specifically Microsoft Outlook, Outlook Express, Windows Mail, and Thunderbird. This solution leverages the power of the community to improve filtering and block spam emails.

SPAMfighter works by teaming up with an extensive network of users who actively flag and report spam. When enough users flag a particular message as spam, it will begin to be automatically filtered for the entire SPAMfighter community. This approach helps to quickly identify and block new threats. In addition, traditional filtering methods including trusted sender lists and blacklists are utilized in this email spam blocker plug-in.

SPAMfighter requires download and installation as an add-on to supported email clients. The installation and configuration process is quite simple and does not require any special technical knowledge, making the program accessible to a wide audience.

Price:
SPAMfighter provides a free version for home use and paid versions for businesses with enhanced functionality and support.

Benefits:

Ease of use and simple integration with popular email clients
Group filtering mechanism that improves protection over time
Free version for personal use

Disadvantages:

Community dependency may mean that some new types of spam will not be blocked immediately
Paid features are required for full business use
Support for a limited number of client applications

CleanMail Home

CleanMail Home is an anti-spam solution designed to block spam emails on home computers. The software can be installed on Windows and works as a mail gateway, i.e. it interposes itself between your email client and the Internet, filtering incoming mail before it reaches your mailbox.

CleanMail Home uses a variety of methods to detect spam, including blacklists, whitelists, sender authentication, content filters (such as keyword checking), and SPF (Sender Policy Framework) support. The program also uses auto-learning techniques while in use to improve filtering.

Price:
CleanMail Home offers a trial version. A full license costs $29.95 per year per user

Benefits:

Does not require any particular expertise to set up and use
Flexible customization of filtering rules

Disadvantages:

Requires installation on the user's computer, which may be less convenient compared to cloud-based or server-based solutions
Suitable for Windows operating system only

SpamSieve

SpamSieve is an email spam blocker program designed specifically for macOS that embeds directly into email clients supported on that operating system. The program uses Bayesian filtering techniques to analyze incoming messages and learns based on feedback from the user.

SpamSieve integrates with a variety of Mac email clients, including Apple Mail, Airmail, Outlook, and other programs. Once installed and configured, SpamSieve runs in the background, analyzing and categorizing incoming emails. When an email client receives a new message, SpamSieve evaluates its content and metadata and determines if the message is spam. If it is, the email is moved to the spam folder.

The key to using SpamSieve is its ability to learn. When a user manually moves erroneously filtered messages from the spam folder back to the inbox or vice versa, the program records these actions and learns, becoming more and more accurate at identifying spam over time.

Price:
SpamSieve is offered as a one-time purchase for $39.99, eliminating the need for monthly or annual payments.

Benefits:

Adaptive Bayesian filtering that takes specifics of the user's correspondence into account
Easy integration with macOS email clients
One-time payment with no recurring charges for license use

Disadvantages:

Only works on macOS
Initial user training is required, which demands some time investment

ChoiceMail

ChoiceMail is spam filtering software that uses a whitelisting system to identify legitimate messages. Unlike traditional filters that analyze each message for signs of spam, ChoiceMail automatically blocks all messages where senders are not on the user's approved contact list or have not been verified.

When a message is received from a new sender, ChoiceMail prompts that sender to undergo verification in order for the message to be delivered. This effectively blocks automated spam, as most spam bots are not equipped to respond to such requests.

Price: The program is offered in various variants, including a free version with basic features and paid versions with advanced features. Detailed price quotes are available on the program's website.

Benefits:

High level of protection from unwanted emails by filtering them through a confirmation system
Automated whitelisting to simplify the contact management process
Ideal for those who prefer a proactive approach to controlling their inbox

Disadvantages:

Possible omission of important messages from new senders who have ignored or missed the confirmation request
Possible miscommunication from contacts who may be confused by confirmation requests for messages they have sent.

Spamihilator

Spamihilator is a free anti-spam email filter software that works with various email clients on Windows. This email spam blocker analyzes and filters incoming messages using a variety of detection methods such as text analysis, probabilistic filters, and a list of trusted senders.

In the communication chain, Spamihilator sits between the email client and the mail server, analyzing and filtering each incoming message. It learns from user preferences and improves its effectiveness over time. Suspicious emails are moved to a special folder where the user can read them and adjust the filtering if necessary.

Spamihilator works with any email client that supports POP3 or IMAP, including Outlook, Thunderbird and other popular applications.

Price: The software is available free of charge.

Benefits:

Highly customizable filters and rules
Free of charge
Ability to learn from user actions

Disadvantages:

Needs initial customization and regular adjustments
May require specific knowledge for best performance
Available for Windows operating systems only

G-Lock SpamCombat

G-Lock SpamCombat is a Windows-based anti-spam filtering solution designed to filter and remove unwanted emails before they are downloaded by your main email client.

G-Lock SpamCombat connects to your mail server via POP3 or IMAP protocols and scans each message for spam using a variety of filters, including Bayesian, DNSBL, and RBL, as well as keywords and phrase-based filters.

Once installed and configured to connect to your email account, G-Lock SpamCombat begins checking incoming messages. Users can view filtered emails in the program to ensure that legitimate messages have not been misclassified as spam in the app’s quest to block spam emails.

Price: At the time this article was being written, version 3.0 of the program was free.

Benefits:

Ease of use due to intuitive interface
Multiple spam filtering methods increase flexibility and efficiency
Ability to review and recover misclassified messages

Disadvantages:

The program is only available for Windows
Pre-loading of emails can take considerable time
Potentially difficult to set up for new users
Lack of automatic learning, unlike systems with Bayesian filters, which adapt over time

Temporary mail to fight spam and more

Using temporary email is a simple and effective answer to the task of how to block junk email from finding its way to your primary inbox while maintaining your email privacy. Here are some of the benefits of using temporary email addresses:

Protecting your primary address from leaks

Using a temporary email address helps prevent your primary email address from being leaked when websites are hacked. In the event of a hack, only your temporary email address will fall into the hands of hackers and spammers, while your primary email address will remain safe. Unfortunately, even well-known and reputable online services are prone to such leaks, so email security measures are never a bad idea.

Privacy protection

Quite often a permanent email address can be matched to the identity of the person to whom it belongs. This can be done using search engines or previously leaked databases. If you need to register on a site you don't trust, your best bet is to use a temporary email address.

No spam

Once your temporary address no longer exists, the ability to send emails to it is gone. And your primary email account continues to function as before, without the added burden of unwanted emails from spammers and long-neglected online services.

One-time use

Temporary mailboxes are ideal for one-time registrations or one-time use scenarios.

Efficiency

Instead of filtering or blocking spam and junk mail in your main mailbox, it's easier to use temporary addresses for untrusted or infrequently used low value resources.