Antispam filter
An antispam filter is a software or hardware-software complex for automatically detecting and blocking unwanted electronic messages (spam) and fraudulent calls, using databases and behavioral analysis.
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What is an antispam filter
Antispam filter is a specialized information security and fintech tool designed to protect users from advertising and fraudulent message flows (SMS, email) and phone calls. Unlike firewalls, which analyze only network packets, the antispam filter works at the application level, evaluating semantic content and metadata.
In simple terms, an antispam filter is like a digital security guard that checks all incoming letters and calls, passing through only those that really matter and blocking everything that looks suspicious: advertising, fraud, phishing, attempts to extort passwords or money.
In the corporate segment, antispam is an obligatory element of secure electronic document workflow, since up to 70% of phishing attacks start with an email. According to Kaspersky Lab, in 2025 the share of spam in total mail traffic in Russia was 45%, and the number of fraudulent calls blocked by antispam systems exceeded 2 billion. Integration of antispam filters with SIEM systems makes it possible to track targeted attacks and account compromises through the analysis of spam-mailing correlation.
How an antispam filter works
Modern antispam filters use a combination of methods for maximum detection accuracy and minimization of false positives:
- Reputation analysis (Black/White Lists): Checking the sender's IP address, domain and identification data against global databases (for example, DNSBL — DNS-based Blackhole List). If the sender is on a black list, the letter is blocked.
- Content filtering: Scanning the text for spam keywords (casino, winnings, subscription renewal, requests for money), as well as analyzing the structure of the letter (presence of suspicious links, attachments, non-standard encoding).
- Behavioral analysis: Machine learning algorithms analyze the sender's behavior: the mass nature of the mailing (number of letters per unit time), the time of sending, the frequency of delivery errors, the nature of changes in the letters.
- Header analysis and authentication: Checking the path of the letter through servers (SPF, DKIM, DMARC) to detect forging of the sender's address. If the letter has not passed the check, it is marked as suspicious.
In mobile devices, antispam is supplemented by analyzing numbers through databases similar to those used in ACS for access verification. Voice recognition technologies are also used to detect fraudulent calls (for example, voice bots).
Types of antispam filters
Antispam filters are classified by installation location, management method and type of protected environment:
- Server (gateway): Installed on enterprise mail servers (for example, Microsoft Exchange, Postfix) and filter all incoming and outgoing traffic before it is delivered to the user's mailbox. They are an obligatory element of secure systems and allow centralized management of security policies.
- Client (desktop): Operate at the level of the user's mail client (for example, built-in MS Outlook, Thunderbird filters) or as plugins. They provide an additional level of protection on the workstation.
- Operator (mobile): Provided by mobile operators (the "Antispam" service for blocking calls and SMS) and are often integrated with the National Payment System "Mir" to confirm transactions and protect against fraud.
- Cloud (SaaS): Provided as a service (for example, Google Postini, Microsoft Exchange Online Protection). They do not require equipment installation, are easily scaled and updated centrally.
The choice of filtration type is important when designing a corporate network, since server antispam unloads workstations and centralizes the management of security policies.
Advantages and role in security
An effective antispam filter gives organizations and users a number of significant advantages in the field of security and productivity:
- Protection against social engineering: Antispam blocks letters trying to extort passwords, bank card data or confidential information (phishing, vishing). This reduces the risk of successful attacks on employees.
- Reducing the load on employees: Eliminates the need to manually sort hundreds of spam letters, which increases productivity and reduces fatigue.
- Protection against malware: Blocks letters with malicious attachments and links to infected sites, preventing infection of the corporate network.
- Control of outgoing traffic: In conjunction with DLP systems, antispam makes it possible to control the transfer of confidential information through external communication channels.
For employees working with state information systems and personal data, the use of certified antispam solutions is often an obligatory regulatory requirement (FSTEC, FSB).
Training employees to recognize spam and phishing is an important part of the overall cybersecurity strategy. The training course helps staff not rely solely on technology, but also develop critical thinking when working with incoming messages.
Frequently asked questions
Where to find an antispam filter on the phone?
In most modern smartphones (Android and iOS), the antispam filter is built into the Phone application. To enable it on Android, go to Settings -> Apps -> Phone -> Caller ID and spam (or a similar section). On iOS: Settings -> Phone -> Silence Unknown Callers. There are also third-party applications (for example, Kaspersky Who Calls, Yandex with Alice, Truecaller) that offer advanced blocking functions. For corporate protection, contact the systems design service.
How to disable the antispam filter?
To disable the antispam filter on Android, go to Settings -> Apps -> Phone -> Caller ID and spam and deactivate the "Filter spam calls" option. On iPhone, a similar option is located in Settings -> Phone -> Silence Unknown Callers. If you use a third-party application (Yandex with Alice, Kaspersky Who Calls), it needs to be disabled in the settings of the application itself or in the phone settings in the "Call blocking and identification" section.
Why do spam calls still come through if the filter is enabled?
Spammers constantly change numbers and bypass black lists, so the filter may let some calls through. It may also depend on the database of your antispam application: if it has not been updated, a new fraudster number may not be recognized. Regularly update your applications and use several levels of protection: for example, a built-in filter + a caller ID from the operator. Fraudsters also use number spoofing, which complicates filtering.
What is antispam in the context of email?
In email, the antispam filter analyzes incoming letters and sorts them: legitimate letters go to the Inbox, suspicious ones to the Spam folder. Corporate filters can automatically delete letters with viruses or malicious links, and also block letters from senders with a bad reputation. Integration with SIEM makes it possible to log all spam incidents for subsequent analysis and configuration of security rules.
Can antispam mistakenly block important letters?
Yes, this is called a false positive. To avoid this, administrators add trusted senders to whitelists and configure the sensitivity of the filter. If an important letter ends up in spam, the user can mark it as "Not spam" — this retrains the filtering algorithm for future messages. In corporate systems, exceptions are also configured for critical counterparties and government bodies.
Is antispam needed at the level of the telecom operator?
Yes, operator antispam blocks mass automated calls and SMS at the network level, before they reach your phone. It is especially relevant for protection against 'probing' calls and fraudsters posing as banks or government bodies. This service is often provided free of charge and is deactivated at the subscriber's request. In Russia, operators actively use antispam systems within the framework of the requirements of Federal Law 38 'On Communications'.
How does antispam help protect business from phishing?
Antispam filters block phishing letters that try to extort passwords, bank card data or confidential information from employees. Modern antispam solutions use ML algorithms to analyze suspicious links, imitation domains and non-standard sender addresses. In conjunction with DLP systems, antispam also controls outgoing messages, preventing data leaks through mail channels.
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Antispam filter
An antispam filter is a software or hardware-software complex for automatically detecting and blocking unwanted electronic messages (spam) and fraudulent calls, using databases and behavioral analysis.
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