Introduction to the problem

We all know what spam is because we have either encountered it or read about it. We all know how spammers collect email addresses. It is also no secret that spam cannot be completely defeated. The problem is how to maximally protect users who leave their contact details on your website with minimal effort.

Previously tested methods of protection

The biggest threat to mailboxes comes from programs that download websites and take mailing addresses from the text of pages. They either download only your site, or wander around like search engines, throughout the network. If your site is small, the following text auto-replacement protection is quite sufficient:

]+href=)([""]?)mailto:(+)()@".
"()(+.(2,4))2([ >])~i", "1"mailto: [email protected]"
onMouseover="this.href="mai" + "lto:3" + "4" + "%40" + "5" + "6";"7", $text); ?>

Unfortunately, it won't work if you have a large site. Let's say spectator.ru, whose author was one of the first to use this method. If I were a spammer, I would go into personal settings, check the “do not show ears” checkbox, 1000 reviews on the page, and catch cookies with Proxomitron. Then, using a rocker or a PHP script, I would download pages with comments (substituting cookies with settings) and use a regular expression to catch the addresses. I would get a small base for advertising mailings.

There were a couple more protection methods in which the mailto: link was automatically replaced with some other one, but the effect remained the same - when you clicked on it, the system client would create a letter to the desired address. Both of them did not stand up to criticism.

Meet the hedgehogs

Obviously, it is difficult to come up with another method of protection other than what has already been tested - providing a form on the site for sending a message. Let's start designing it. The advantages of this method are obvious: no one will be able to get addresses for their spam database from your website. It will not be possible to send messages by hiding your address, as spammers do - the web server will record its IP address. Lists of public anonymous proxy servers are regularly updated, and it is easy to block access from them.

Form sender

Let's start with this, because this is the most difficult part.

When installing a form sender on a site, it is important to protect it from hooligan attacks, which can be no easier than spam. Therefore, we will have to make great efforts in this direction.

First, let's protect ourselves from stupid double clicks and sending many identical requests. The idea is this: the message will not be sent if the user has not previously opened the page with the form, and by opening the page with the form, the message can be sent only once. This can be done using sessions built into PHP. When opening a page with a form, we will launch a session in which we will save a variable, say $flag. We will display the session ID as a hidden element at the very end of the form. The user enters a message and submits the form. Upon receiving the form, the script starts a session and checks the presence and value of the $flag variable. If the variable does not exist, then this is a repeated click, the letter is not sent and an error message is displayed. If the variable exists, and the form data suits us (the required fields are filled in), the script sends a letter and deletes the session.

Secondly, let’s protect ourselves from smart hooligans by recording message logs. If the user submits a correctly filled out form, the script will look at the logs and check what is there. Yes, it should be banned

* send messages to the same address more often than a certain period
* send the same text to different addresses
* and simply use the form sender too often - say, no more than 10 messages per day per user

We display the session ID at the very end of the form, so that the hacker would need to download the entire form and parse it, which is more complicated than simply sending HTTP requests. Naturally, the form sender will issue messages about errors in writing the message, a requirement to indicate a return address, etc.

The resulting form sender code turned out to be too large to include in the text. It has been archived on the website. It seems that the script is working and sending messages.

Replacing addresses in text

Now the form sender is ready, and you need to replace all emails with links to it. Of course, you shouldn't do this manually. For myself, I wrote a script that automatically replaces addresses with links to the form sender.

...Disadvantages: more time for arranging links (compensated by the directory of links), the user, when hovering the cursor over a link, does not see what address he will go to. (Dmitry Smirnov, “Ideal author’s project, hypertextuality”)

All the mentioned disadvantages can be easily eliminated if you use code similar to the one I will now describe and show.

There is nothing complicated here; if these are links, then “more time for arrangement” is not required. On my site I use an engine script that is called by all pages, so it’s not a problem to add code to it or call it from it that replaces addresses. Mailing addresses were and are written directly in the text of the pages, but before being displayed to the user they are replaced with the required text. Compiling a database of links or email addresses is not a problem.

So what does an address replacer do? It searches the text for “mailto:” links, selects addresses from them, sends a query to the database to count (count(*)) how many addresses from those on the page are in a special table. If there are new addresses on the page, then their number will be greater than the query result. In this case, a query is made in which address values ​​are selected, and those already existing in the table are excluded from the list. The remaining list is sent to the table using an INSERT query.

As for ID addresses, in my opinion it is better to use something that a site visitor could not find. Can you imagine the link /email.php?id=10 leading to the form sender? What a temptation to put 11, 12, etc. there. and try sending them all a message. Therefore, I decided to use the md5 hash of the addresses as identifiers. It’s unlikely that anyone will undertake to select the hash. In the case of a directory of links, you can get by with ID, but then you have to select all the values ​​from the database, and replacing addresses with their hashes is much simpler.

A command of the form is executed

]+href=)". "([""]?)mailto:(+@+". ".(2,4))2(.*?>)~ie", ""12"/email.php ?email=". urlencode(md5("3")). ""4"", $text); ?>

...which replaces addresses with their hashes. I did not dare replace the remaining addresses in the text with links, but made a simple replacement with addresses like vasya_at_pupkin_dot_ru. The autoreplacement code is also in the archive.

Bottom line

Hiding email addresses from visitors is quite easy. The autocorrect mechanism does not require additional effort, and you can continue writing site pages as if nothing had happened. Difficulties arise when protecting the form sender from web hooligans. This protection requires a lot of effort and complex code, so I have not yet used written code on the site. You can download an archive with an address substitute and a form sender, but I ask you very much: do not put it on your site in the form in which you downloaded it, I myself don’t know how reliably it works.

- €55-250 million annually. 60% global mail traffic.
50-75% from all Russian mail traffic. Modern anti-spam tools filter 85-98% of spam. The global sales market for antispam filters and services in 2004 was approximately $500 million (according to IDC estimates).
Most antivirus vendors have included antispam components in their products. During the year, there were several acquisitions of anti-spam software manufacturers by anti-virus companies (in particular, the purchase of BrightMail by Symantec for $340 million). In Russia, anti-spam filters were installed by the majority of holders of public mail services and the majority of providers, which made it possible to alleviate the severity of the spam problem for their clients. The undoubted leader in Russia in terms of sales volume and number of protected mailboxes is Spamtest technology.
1. PREVENTION#1 way to fight spam is to protect your address. If spammers don't know your address, there will be no spam. If your address appears on the Internet, you will have to throw it away and create a new one, it will only be a matter of time. And, as a result, you have to inform all your friends and partners again of the new address, and you may lose a number of contacts. To prevent this from happening Create two email addresses. One address for long-term contacts (don’t post it online).
Another address for making contacts, using the network (chat rooms, bulletin boards, etc.).
Then there should be no spam at the first address, because it is not known on the network.
When spam arrives at the second address, just throw it away and create a new one.
2. SELECTING A NAME People strive to get the most concise address. Let's say sergey@mail.ru is cool and what a pity that all the simple addresses are already taken. Rest assured that [email protected] spam is pouring in non-stop. It’s cool to have a laconic site name, but the email address will still have to be communicated to everyone personally, even if it is from numbers or original, not a hackneyed word. By the way, for this purpose, the leading mail gmail.com registers names of at least 6 characters. All short names have long been included in spam lists.
3. HTML SPECIAL CHARACTERS The simplest and most commonly used method of protection against spiders is address encoding Email by using HTML special characters. Instead of a dog - @ . But today this method is hopelessly outdated.
Robots easily find such addresses.
4. JAVASCRIPT On the anti-spam code generator page you can generate your own script. Since these scripts for hiding addresses are created at home, they are very diverse and there are no programs that can extract email from JavaScript. Today this is the most reliable address protection on the network.
5. ANTI-SPAMMERS But what if you are exposed, or you are so famous that it is impossible for you not to be exposed, you cannot do without an antispammer. There are many anti-spammer programs, you can download them online.
What I don’t recommend doing.
I came to the conclusion that all these antispams are small and weak, and a person cannot handle a sensible antispam; only a reputable company, say, such as Gmail.com, can do this. Their spam remains on the server, you can always go in and correct it. So my strong advice: get yourself an email account on Google.
I have never seen a better spam filter; all spam remains on the server, which can always be viewed and corrected if desired. Antispammers do not completely solve the problem, but make life easier with the problem.
6. POCKET PC AND WAP Spam has reached this level, but today there are fairly reliable means of protection. Therefore, the development of this issue is not relevant.

Spam is the mass sending of messages to users who have not consented to receive them. Carried out for the purpose of advertising certain products, disseminating information, stealing personal data, etc. This is intrusive advertising of something. In most cases, spam is presented in the form of mailings emails, but in fact it is used wherever there is open access to the dissemination of information: social media and media, forums, comments on websites, instant messengers, emails, SMS to phone. Even in the offline space there is spam. For example, promotional brochures in your mailbox. People who send spam messages are called spammers. Spam advertising is one of the cheapest methods of online promotion, but not the most effective. Such mailing is perceived negatively by the audience, which prevents all companies from using it. Those who value their reputation and image do not use spam.

Where does the word "spam" come from?

The word “spam” first appeared in the 40s of the 20th century, in the post-war period. Initially, it meant the name of canned food included in the meat ration of soldiers. After the war, they had to be urgently sold before the expiration date expired and they spoiled. This led to the fact that advertising for this product was everywhere: on the streets, in newspapers, in transport. It was deliberately made aggressive, imposing on people the need to purchase these canned foods. It was this event that came to mind when this kind of advertising began to be actively used on the Internet. Aggressive and intrusive sending of advertising messages is appropriately called spam. Since then, the word “spam” has meant “mass sending of intrusive advertising.” The user did not ask, did not subscribe, but they send him letters in the contents of which he is not interested. At first (as soon as the Internet and email appeared), spam advertising on the Internet was more effective than it is now. People were not used to this, and advertising “blindness” did not yet exist. But it still remains one of the most inexpensive ways to reach the maximum audience, which allows it to remain afloat as one of the most popular ways to promote your services and products.

A spam attack is the sending of spam messages with increased concentration on certain sites or channels. For example, spammers have discovered that a certain forum has a high return rate. This information spread through spam circles, and the site was hit with a huge wave of messages with intrusive advertising. This event is called a spam attack. Spamming attacks are not always carried out due to the high impact of the site. Sometimes they happen due to someone’s malicious intent with the aim of harming the site and its owner. For example, they are carried out by unscrupulous competitors.

Types of spam

All spam can be classified according to several criteria.

By area of ​​distribution:

online spam – distributed in the online space;

offline spam – distributed in the offline space.

By distribution method:

manual – messages are sent manually.

By degree of danger:

Most popular sites and electronic mailboxes have sufficient protection against dangerous spam. They use spam filters. Messages that can cause real harm are blocked automatically. The most dangerous of them are deleted permanently, less dangerous or simply dubious ones are placed in the Spam folder. Often, the system mistakenly places messages in the Spam folder that do not cause any harm to the user, for example, a letter confirming registration on a website. For the system, these are unfamiliar sources, therefore, it does not trust them. Therefore, regularly check your Spam folder and remove the necessary messages from there.

Safe

commercial advertising. Includes sending messages advertising various types of goods, services, websites, etc. As mentioned earlier, spam mailing is one of the most inexpensive ways to promote on the Internet. Hence, it is in demand among online entrepreneurs. They simply chose spam as one of their promotion channels;

advertising that is prohibited by law. Russian legislation contains a list of goods and services that are prohibited from advertising. Most popular channels (search engines, social networks) adhere to these requirements, and sometimes add their own. This causes certain difficulties for advertisers. Electronic mailing does not have such restrictions, which allows advertisers to freely advertise any products and in any form;

manipulation of public opinion. Spam is often used as a tool to influence the public opinion of the audience. These are not only political motives, but also commercial ones. For example, someone decided to send out compromising material about a competitor or send out mailings on someone else’s behalf in order to receive a negative reaction in return. Such mailings do not harm users, but can cause certain sentiments in society;

• mailing with a request to forward the message. A particularly popular type of spam on social networks. As a rule, it does not carry any meaning and does not pursue any goals. These are messages in the spirit of “Forward this letter to 20 friends and next year you will find the love of your life.” Oddly enough, there are people who continue to do this. Rarely may contain hidden advertising.

Dangerous (malicious)

This type of spam can cause real harm to users - steal their personal data (logins, passwords), gain access to electronic wallets, infect the computer with viruses, etc. Most often, the contents of such letters include links or attachments. Do not click on them or download them under any circumstances. Types of dangerous spam:

Places of distribution

Where can you find spam?

Email is the most common place for spam messages. Letters are not moderated before being sent, therefore their content is not limited in any way. As a rule, spam filters are used after sending.

Forums – those sites where there is no moderation are very popular among spammers, as this allows you to freely publish any information. Forums where all messages are verified are not used at all or are used to publish hidden advertising.

Comments on sites - similar to forums, those sites where there is no moderation are increasingly popular among spammers.

Social networks are for Lately The number of spam messages on social networks has only increased. Personal messages and comments are the most popular tool for disseminating information. Spam on social networks is characterized by greater “friendliness”. Senders, as a rule, do not just send you an advertising message, but try to enter into a dialogue and get to know each other. Of course, such an unexpected desire to communicate is caused only by commercial purposes - to sell a product or service.

Messengers – in recent years, with the growing popularity of instant messengers (Viber, Telegram, WhatsApp), the number of spam messages in them has also increased.

SMS – probably everyone has received an SMS with an advertisement on their phone from unknown numbers. This is spam.

How spammers find mailing addresses

One of the most popular questions is “How do spammers know my address or phone number?” Finding user contacts is not a big problem. You can get them in several ways.

Based on the above, the conclusion suggests itself: do not leave your contact information anywhere. Create several email addresses - one for important correspondence and important services, the other for everything else. If spam catches up with you, then let it be in the second mailbox.

How to disable spam

In some cases, it is easy to disable spam - just click the “Unsubscribe” button in the letter. The method works if you yourself once subscribed to the source. Sometimes a subscription is issued automatically after registering on the site.

But be careful. Sometimes spammers design links as an “Unsubscribe” button. Of course, after clicking, no unsubscribe will occur. You will simply be transferred to the promoted resource. If the source seems unfamiliar to you, it is better to use in the following way and block it to get rid of annoying emails. In most email services, as well as in social networks, you can block addresses and users from whom unwanted emails come. How to block spam (using Gmail as an example):

Ready! After these steps, the selected address will not be able to send you letters. Now he is blacklisted. Similar actions can be performed on social networks.

Anti-spam methods

To avoid having to block each spammer manually (after all, there can be hundreds of sources), just follow simple tips and anti-spam recommendations.

Do not publish your address and contacts in public or dubious places.

Create a second mailbox for unimportant messages and use it.

Do not download files as attachments.

Use only popular email services (in them maximum level spam protection).

Create a more complex mailing address. The lighter the address, the easier it is for spammer programs to generate it.

The most secure mailboxes

In terms of protection from spam mailings, the most secure mailboxes are:

Google mail (gmail);

Yandex mail;

Mail.ru-mail.

It is important to understand that no service will provide 100% protection. Promotional emails will always slip through. After all, spam methods are improving every year, becoming more sophisticated and secretive; spammers are constantly finding new ways to bypass filters. But the services described above are capable of minimizing the number of unwanted messages.

Hello, dear readers of the blog site. Surely you have already encountered spam, even if you didn’t know exactly what this outrage is called. And for this it is not even necessary. Spam also pours into your regular mailbox with enviable regularity - these are the same countless advertising booklets that are slipped to you in the hope that you will order or buy something.

So, spam is that is precisely the annoying one, creeping in from all sides advertising(but not only advertising - there are worse things). You didn’t order it, you don’t need it, but he rushes and rushes from every corner. In this heap, the information you need can easily get lost and you have to spend a lot of time sifting through it.

In our computer age, the main source of spam. And besides advertising spam mailings can also be dangerous both for your wallet (phishing, social engineering, scams) and for your computer (viruses, worms, Trojans).

What does the word Spam mean, what does it look like and how can you fight it, you will find out by looking at this short article. I hope it will be interesting (well, certainly useful - I promise you that).

Spam - what is it?

What does the word SPAM mean?

Self word Spam comes from the name of canned meat, which was vigorously advertised after the end of the Second World War (obviously, it was necessary to urgently sell out the soldiers' meat rations).

The advertising was so aggressive, comprehensive and ubiquitous that this word (and the “sediment” associated with it) was remembered, but only because of the intrusive advertising that appeared along with it in conferences (then still on the Fidonet, if anyone remembers).

The word stuck, especially since intrusive advertising did not become less, but rather the opposite. When email gained popularity, unauthorized mass advertising and malicious mailings became commonplace. Such mailings were profitable for spammers, because the necessary information was communicated to a large number of people without any special costs.

But It's not limited to email. They spam in private messages on social networks, on forums, in instant messengers instant messages, on message boards, in comments to blogs, open for editing and adding text by anyone. They will also spam your phone, for example by calling you advertising or sending advertising SMS messages.

Where can you find him on the Internet?

1. Email- it's just a Klondike for spammers. With the help of mass mailings you can sell anything, you can deceive and rob, you can infect computers and send worms. Databases for mass mailings are collected independently (with the help of programs), or purchased from those who do this professionally.
2. Forums, comments blogs, wiki sites and message boards - here, essentially, everyone is allowed to leave messages and spammers find it difficult to resist spamming. This is not always advertising - often in this way, webmasters try to get a free link to their site so that it ranks higher in the Yandex or Google search results for various queries. This brings them traffic and money.
3. Social media and dating sites - spam is very common among incoming personal messages. It is also available in the comments to messages.
4. Messengers (like ) are also susceptible to this scourge.
5. SMS-messages from people unknown to you of an advertising nature. Probably everyone is familiar with it.
6. Search spam- a rather specific thing, but familiar to everyone. Have you ever had a situation where you enter a query into Yandex (Google), and the responses are entirely sites with some kind of bullshit that have nothing to do with the matter. These are so-called doorways (sites with automatically generated useless texts). They spam search engine results, but they make money from visitors visiting them (in different ways).

Those. all letters in your mailbox (or forum messages, blog comments, personal messages) of an advertising or other nature from a sender unknown to you - this is spam. True, the newsletters you have subscribed to can also be intrusive, but you can still unsubscribe from them (refuse to receive them further).

Spam itself is annoying and annoying, because it litters where it appears. Most often, this is your inbox, and it can be quite difficult to separate the wheat from the chaff when there are too many unwanted messages. But spam can also pose a real danger to both you and your computer. Let's figure this out.

Understanding the types of spam (harmless and dangerous)

From now on I will mainly talk about spam messages arriving by email, because it is this channel that is considered especially susceptible to this phenomenon. Everything else is not as neglected and is not so actively used by spammers, and this does not apply to all network users. But the problem of protecting them from unwanted messages is acute.

Types of harmless spam

1. Advertising of legal goods and services- in this case, the business owner simply chose spam mailings as one of the channels for attracting clients and customers, because it is not expensive, fast and brings results. Naturally, he doesn’t think much about the moral (or rather immoral) side of this matter.
2. Prohibited advertising— there are goods and services that are prohibited by law from advertising, and for them spam mailings can be the main channel for attracting customers. By the way, spammers also advertise their services through mass mailings, since this activity is prohibited by law. This also includes advertising that discredits competitors, since this is also prohibited by law (praise yourself, but don’t scold others).
3. Impact on public opinion— very often spam becomes a good choice for those who are trying to manipulate public opinion in the desired direction. It could be politics, but it could also be. Letters in general can be sent supposedly from some person in order to compromise him, change his opinion about him, or use his authority for profit. But this does not pose a danger to you personally.
4. Letters that ask to be forwarded to others- these can be varieties of so-called “letters of happiness” (send it to 10 friends and you will be happy), or asking to send information to friends for some other reason. Often such letters are used by spammers to collect or replenish an existing email database for subsequent mass mailings.

High-risk spam - what it can be

While regular (harmless) spam may only have a slight impact on your peace of mind and mental health, the examples below can be quite dangerous for your wallet or computer. And this is no joke.

I myself (the one who teaches and trains everyone) a couple of years ago “bought” a similar type of letter (phishing) and parted with several thousand rubles (read “”). I just got wrapped up and did everything “automatically” just to get behind, well, when I realized it, it was too late.

1. - a very effective method of deceiving not only gullible, but also simply busy or inattentive people (there is a hook for everyone). They send you a letter supposedly from your bank, electronic money service, or somewhere else. In this letter, you will definitely be taken aback by something (unsettled) and asked to log in to the site to solve the problem. You log in, but the site will be fake (although it looks exactly like the real one) and the data you provided will be immediately used to steal all your money.
2. Nigerian letters- you learn that you can get a large amount of money (various pretexts - from an unexpected inheritance to helping a prince in exile). You don’t believe it for a long time, but they convince you. When you believe it, you will be asked to transfer some money for “related expenses.” You translate and no one will bother you anymore.
3. Viruses, worms, Trojans— the letter may contain an attached file with malware(or a link leading to a site with a virus). She can immediately cause problems with the operation of the computer, or she will sit quietly in a corner and carefully write down all the passwords, logins and other useful household things you enter. Worms, among other things, also know how to send themselves to your friends using the email addresses found in your contacts (as they will later call you...).

Spam protection

Where do spammers get databases with email addresses?

1. Spammers (those who produce mass mailings) collect email addresses from all available sources. These can be forums, guest books, chats, social networks and other sites where postal addresses can be publicly available.
2. Hackers manage to get to some databases of addresses stored on websites.
3. Collecting Emails is carried out in most cases programmatically (with the help of search bots - harvesters) and this does not require much effort (only time, and even then not very much). Moreover, similar spam email databases You don’t have to collect them, but buy them from those who specialize in this matter ().
4. There are billions of email addresses registered all over the world, and therefore you can simply try to generate Emails using special programs using appropriate dictionaries. With a high degree of probability, many of them will actually exist. Read below about how spammers check the reality of addresses.
5. There are special worms (viruses) that can send themselves to a database of addresses found on the victim’s computer. The database collected in this way will already be cleared of non-working mailboxes.

How do spammers clean databases of inactive email addresses?

Those who collect a database of addresses essentially don’t care who owns this or that address - they send letters to everyone, because there will still be someone who will respond to them (as they say - they hit the squares).

But still, in order to optimize costs and increase the return on mailings, it is beneficial for them to clear the databases of non-existent addresses. How do they do it? Let's get a look.

1. The simplest thing is to place a picture in the letter (maybe not even visible - one pixel in size), which will be loaded from the site owned by the spammer when the user opens the letter. If the picture is loaded, it means the letter was opened and the email is valid.
2. Many email clients (programs for working with email) automatically send a message that the letter has been read, which again plays into the hands of spammers.
3. The letter may contain a link urging you to go somewhere, promising mountains of gold. We've moved on - consider that your Email will now be marked as valid. The most unpleasant thing is that such a link can be disguised as an unsubscribe button, which will actually lead to the opposite effect.

How to reduce the likelihood of your email getting into the spam database?

In general, as soon as your mailbox is “verified,” spammers won’t just leave you. It is important to understand that no one is immune from spam. But it is possible significantly reduce the likelihood of getting into such a spam database if you take the following precautions:

1. You can, of course, not publish your Email anywhere at all and not tell it to anyone. But in most cases this is difficult to do, so I advise except the main drawer have one or two minor ones that you will use to register on forums, etc. Often they can also come in handy, which can be obtained without registration at all.
2. Do not click on links in spam emails (even if there is an “Unsubscribe” button - this is a trap) and, if possible, disable automatic download images in the email client program you are using. There is a chance that your Email will be counted as inactive and mass mailings will not arrive at hundreds per day.
3. If you have not yet registered a mailbox or are planning to create a new one (for example, because the old one is completely clogged with spam), then do not proceed from the convenience and ease of remembering it, but on the contrary, make it longer and more complex. To your friends, you will still send it to in electronic format, but spammer search programs are unlikely to guess it.

What to do if spam no longer lets you breathe?

These were all preventive measures to combat spam (or rather, reduce its quantity). But there is the possibility of an effective fight even in an already completely neglected situation. In this case, it becomes extremely important.

The fact is that in such large services as or, there are powerful antispam filters.

They place all suspicious emails in a separate Spam folder, thereby freeing the Inbox from junk. Yes, there is no perfect spam cutter, and whenever possible, before cleaning, it would be better to view the contents of the Spam folder diagonally to see if it contains legitimate correspondence. But it’s still much easier than digging through all this garbage all the time.

If you have a mailbox on another service, where the spam cutting is poor (for example, as in), then you shouldn’t despair. Get yourself an Email on Gmail or Yandex, and then set up mail forwarding to it from your old mailbox. Moreover, these settings can be made as in the old mailbox (i.e. set up forwarding - shown in the screenshot):

Also, in the new mailbox, you can configure the collection of mail from your existing Emails (the screenshot shows the settings for collecting mail in Gmail):

The same can be said about email client programs. Most of them also have a built-in spam cutter.

But in this case we should not forget that the mail service will have its own spam folder. this can be corrected in the settings of the service or client program).

Good luck to you! See you soon on the pages of the blog site

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What methods are there to combat spam?

There are two main methods of protecting a mail server from spam: protecting against spam when it is received by the mail server, and separating spam from the rest of the mail after it is received by the mail server.

Among the first method, the most popular methods are the use of DNS Black List (DNSBL), Greylisting and various delays when sending mail; use of various technical means, such as checking the existence of a user on the sending side (callback), checking the “correctness” of the sending server using methods such as the presence of a record in the reverse DNS zone, the legality of the name when establishing an SMTP session (helo), checking the SPF record (for this to work in the DNS record about the host, the corresponding entry about the legitimate sender servers is used).

Among the methods of analyzing the content of a letter, the most popular methods are checking using various algorithms, such as searching for special keywords advertising or based on Bayes' theorem. The algorithm based on Bayes' theorem contains elements of probability theory, is initially trained by the user on messages that, in his opinion, are spam, and subsequently separates messages that contain spam based on characteristic features.

So, let's take a closer look at these email filtering methods.

Black lists or DNSBL (DNS Black Lists)

Blacklists include addresses from which spam is sent. Widely used lists are “open relays” and “open proxies”, and various lists of dynamic addresses that are allocated by providers to end users. Due to their ease of implementation, the use of these blacklists is done through the DNS service.

Gray lists or greylisting

The operating principle of greylisting is based on spamming tactics. As a rule, spam is sent in a very short time in large quantities from some server. The work of a gray list is to deliberately delay the receipt of letters for some time. In this case, the address and time of forwarding are entered into the gray list database. If remote computer is a real mail server, it must store the letter in a queue and resend it within five days. Spambots, as a rule, do not save letters in the queue, so after a short time they stop trying to forward the letter. It has been experimentally established that on average the time it takes to send spam is a little more than an hour. When resending a letter from the same address, if the required amount of time has passed since the first attempt, the letter is accepted and the address is added to the local white list for a sufficiently long period.

Performance Analysis

The first two methods allow you to filter out about 90% of spam at the stage of delivery to the mailbox. Already delivered mail can be marked by means of analyzing the contents of the letter, for example, using the SpamAssassin program. This product allows, based on special algorithms, to add corresponding lines to the headers of letters, and the user, based on mail filters, mail client, can filter mail to required folders mail program.

Conclusion

Of course, there are other methods of protecting against spam, the most effective, unfortunately, on this moment are preventive measures, such as not leaving your real email account on websites, forums and message boards, using temporary addresses for such needs, which can later be deleted if publication is necessary mailbox on the site, use graphics and similar measures instead of text.

You can connect and configure GreyListing through the ISPmanager panel in the "Features" section

You can find out more about setting up anti-spam methods through the control panel here DNSBL and here Greylisting.