diff --git a/EmailValidator/Helper/SmtpSocketHelper.php b/EmailValidator/Helper/SmtpSocketHelper.php
new file mode 100644
index 0000000..9e0c2de
--- /dev/null
+++ b/EmailValidator/Helper/SmtpSocketHelper.php
@@ -0,0 +1,100 @@
+<?php
+
+namespace Egulias\EmailValidator\Helper;
+
+class SmtpSocketHelper
+{
+    /**
+     * @var int
+     */
+    private $port;
+
+    /**
+     * @var int
+     */
+    private $timeout;
+
+    /**
+     * @var resource
+     */
+    private $handle;
+
+    public function __construct($port = 25, $timeout = 15)
+    {
+        $this->port = $port;
+        $this->timeout = $timeout;
+    }
+
+    /**
+     * Checks is resource
+     *
+     * @return bool
+     */
+    public function isResource()
+    {
+        return is_resource($this->handle);
+    }
+
+    /**
+     * Opens resource
+     *
+     * @param string $hostname
+     * @param int $errno
+     * @param string $errstr
+     */
+    public function open($hostname, &$errno, &$errstr)
+    {
+        $this->handle = @fsockopen($hostname, $this->port, $errno, $errstr, $this->timeout);
+    }
+
+    /**
+     * Writes message
+     *
+     * @param string $message
+     *
+     * @return bool|int
+     */
+    public function write($message)
+    {
+        if (!$this->isResource()) {
+            return false;
+        }
+
+        return @fwrite($this->handle, $message);
+    }
+
+    /**
+     * Get last response code
+     *
+     * @return int
+     */
+    public function getResponseCode()
+    {
+        if (!$this->isResource()) {
+            return -1;
+        }
+
+        $data = '';
+        while (substr($data, 3, 1) !== ' ') {
+            if (!($data = @fgets($this->handle, 256))) {
+                return -1;
+            }
+        }
+
+        return intval(substr($data, 0, 3));
+    }
+
+    /**
+     * Closes resource
+     */
+    public function close()
+    {
+        if (!$this->isResource()) {
+            return;
+        }
+
+        @fclose($this->handle);
+
+        $this->handle = null;
+    }
+}
\ No newline at end of file
diff --git a/EmailValidator/Validation/Error/IllegalMailbox.php b/EmailValidator/Validation/Error/IllegalMailbox.php
new file mode 100644
index 0000000..1b6646e
--- /dev/null
+++ b/EmailValidator/Validation/Error/IllegalMailbox.php
@@ -0,0 +1,49 @@
+<?php
+
+namespace Egulias\EmailValidator\Validation\Error;
+
+use Egulias\EmailValidator\Exception\InvalidEmail;
+
+class IllegalMailbox extends InvalidEmail
+{
+    const CODE = 995;
+    const REASON = "The mailbox is illegal.";
+
+    /**
+     * @var int
+     */
+    private $responseCode;
+
+    /**
+     * IllegalMailbox constructor.
+     *
+     * @param int $responseCode
+     */
+    public function __construct($responseCode)
+    {
+        parent::__construct();
+
+        $this->responseCode = $responseCode;
+    }
+
+    /**
+     * @return int
+     */
+    public function getResponseCode()
+    {
+        return $this->responseCode;
+    }
+
+    /**
+     * @return string
+     */
+    public function __toString()
+    {
+        return sprintf(
+            "%s SMTP response code: %s. Internal code: %s.",
+            $this->message,
+            $this->responseCode,
+            $this->code
+        );
+    }
+}
diff --git a/EmailValidator/Validation/MailboxCheckValidation.php b/EmailValidator/Validation/MailboxCheckValidation.php
new file mode 100644
index 0000000..97e3f71
--- /dev/null
+++ b/EmailValidator/Validation/MailboxCheckValidation.php
@@ -0,0 +1,181 @@
+<?php
+
+namespace Egulias\EmailValidator\Validation;
+
+use Egulias\EmailValidator\EmailLexer;
+use Egulias\EmailValidator\Exception\InvalidEmail;
+use Egulias\EmailValidator\Helper\SmtpSocketHelper;
+use Egulias\EmailValidator\Validation\Error\IllegalMailbox;
+use Egulias\EmailValidator\Warning\NoDNSMXRecord;
+use Egulias\EmailValidator\Warning\SocketWarning;
+use Egulias\EmailValidator\Warning\Warning;
+
+class MailboxCheckValidation implements EmailValidation
+{
+    const END_OF_LINE = "\r\n";
+
+    /**
+     * @var InvalidEmail
+     */
+    private $error;
+
+    /**
+     * @var Warning[]
+     */
+    private $warnings = [];
+
+    /**
+     * @var SmtpSocketHelper
+     */
+    private $socketHelper;
+
+    /**
+     * @var string
+     */
+    private $fromEmail;
+
+    /**
+     * @var int
+     */
+    private $lastResponseCode;
+
+    /**
+     * MailboxCheckValidation constructor.
+     *
+     * @param SmtpSocketHelper $socketHelper
+     * @param string $fromEmail
+     */
+    public function __construct(SmtpSocketHelper $socketHelper, $fromEmail)
+    {
+        if (!extension_loaded('intl')) {
+            throw new \LogicException(sprintf('The %s class requires the Intl extension.', __CLASS__));
+        }
+
+        $this->socketHelper = $socketHelper;
+        $this->fromEmail = $fromEmail;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getError()
+    {
+        return $this->error;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getWarnings()
+    {
+        return $this->warnings;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function isValid($email, EmailLexer $emailLexer)
+    {
+        $mxHosts = $this->getMXHosts($email);
+
+        $isValid = false;
+        foreach ($mxHosts as $mxHost) {
+            if ($this->checkMailboxExists($mxHost, $email)) {
+                $isValid = true;
+                break;
+            }
+        }
+
+        if (!$isValid) {
+            $this->error = new IllegalMailbox($this->lastResponseCode);
+        }
+
+        return $this->error === null;
+    }
+
+    /**
+     * Gets MX Hosts from email
+     *
+     * @param string $email
+     *
+     * @return array
+     */
+    protected function getMXHosts($email)
+    {
+        $hostname = $this->extractHostname($email);
+
+        $result = getmxrr($hostname, $mxHosts);
+        if (!$result) {
+            $this->warnings[NoDNSMXRecord::CODE] = new NoDNSMXRecord();
+        }
+
+        return $mxHosts;
+    }
+
+    /**
+     * Extracts hostname from email
+     *
+     * @param string $email
+     *
+     * @return string
+     */
+    private function extractHostname($email)
+    {
+        $variant = defined('INTL_IDNA_VARIANT_UTS46') ? INTL_IDNA_VARIANT_UTS46 : INTL_IDNA_VARIANT_2003;
+
+        $lastAtPos = strrpos($email, '@');
+        if ((bool) $lastAtPos) {
+            $hostname = substr($email, $lastAtPos + 1);
+            return rtrim(idn_to_ascii($hostname, IDNA_DEFAULT, $variant), '.') . '.';
+        }
+
+        return rtrim(idn_to_ascii($email, IDNA_DEFAULT, $variant), '.') . '.';
+    }
+
+    /**
+     * Checks mailbox
+     *
+     * @param string $hostname
+      * @param string $email
+     * @return bool
+     */
+    private function checkMailboxExists($hostname, $email)
+    {
+        $this->socketHelper->open($hostname, $errno, $errstr);
+
+        if (!$this->socketHelper->isResource()) {
+            $this->warnings[SocketWarning::CODE][] = new SocketWarning($hostname, $errno, $errstr);
+
+            return false;
+        }
+
+        $this->lastResponseCode = $this->socketHelper->getResponseCode();
+        if ($this->lastResponseCode !== 220) {
+            return false;
+        }
+
+        $this->socketHelper->write("EHLO {$hostname}" . self::END_OF_LINE);
+        $this->lastResponseCode = $this->socketHelper->getResponseCode();
+        if ($this->lastResponseCode !== 250) {
+            return false;
+        }
+
+        $this->socketHelper->write("MAIL FROM: <{$this->fromEmail}>" . self::END_OF_LINE);
+        $this->lastResponseCode = $this->socketHelper->getResponseCode();
+        if ($this->lastResponseCode !== 250) {
+            return false;
+        }
+
+        $this->socketHelper->write("RCPT TO: <{$email}>" . self::END_OF_LINE);
+        $this->lastResponseCode = $this->socketHelper->getResponseCode();
+        if ($this->lastResponseCode !== 250) {
+            return false;
+        }
+
+        $this->socketHelper->write('QUIT' . self::END_OF_LINE);
+
+        $this->socketHelper->close();
+
+        return true;
+    }
+}
\ No newline at end of file
diff --git a/EmailValidator/Warning/SocketWarning.php b/EmailValidator/Warning/SocketWarning.php
new file mode 100644
index 0000000..05072ab
--- /dev/null
+++ b/EmailValidator/Warning/SocketWarning.php
@@ -0,0 +1,13 @@
+<?php
+
+namespace Egulias\EmailValidator\Warning;
+
+class SocketWarning extends Warning
+{
+    const CODE = 996;
+
+    public function __construct($hostname, $errno, $errstr)
+    {
+        $this->message = "Error connecting to {$hostname} ({$errno}) ({$errstr})";
+    }
+}
diff --git a/Tests/EmailValidator/Validation/MailboxCheckValidationTest.php b/Tests/EmailValidator/Validation/MailboxCheckValidationTest.php
new file mode 100644
index 0000000..5ef87ce
--- /dev/null
+++ b/Tests/EmailValidator/Validation/MailboxCheckValidationTest.php
@@ -0,0 +1,67 @@
+<?php
+
+namespace Egulias\Tests\EmailValidator\Validation;
+
+use Egulias\EmailValidator\EmailLexer;
+use Egulias\EmailValidator\Helper\SmtpSocketHelper;
+use Egulias\EmailValidator\Validation\Error\IllegalMailbox;
+use Egulias\EmailValidator\Validation\MailboxCheckValidation;
+use Egulias\EmailValidator\Warning\NoDNSMXRecord;
+use PHPUnit\Framework\TestCase;
+
+class MailboxCheckValidationTest extends TestCase
+{
+    public function testValidMailbox()
+    {
+        $socketHelperMock = $this->getMockBuilder(SmtpSocketHelper::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $socketHelperMock
+            ->expects($this->any())
+            ->method('isResource')
+            ->willReturn(true)
+        ;
+
+        $socketHelperMock
+            ->expects($this->any())
+            ->method('getResponseCode')
+            ->willReturnOnConsecutiveCalls(220, 250, 250, 250)
+        ;
+
+        $validation = new MailboxCheckValidation($socketHelperMock, 'test@validation.email');
+
+        $this->assertTrue($validation->isValid('success@validation.email', new EmailLexer()));
+    }
+
+    public function testDNSWarnings()
+    {
+        $validation = new MailboxCheckValidation(new SmtpSocketHelper(), 'test@validation.email');
+        $expectedWarnings = [NoDNSMXRecord::CODE => new NoDNSMXRecord()];
+        $validation->isValid('example@invalid.example.com', new EmailLexer());
+        $this->assertEquals($expectedWarnings, $validation->getWarnings());
+    }
+
+    public function testIllegalMailboxError()
+    {
+        $socketHelperMock = $this->getMockBuilder(SmtpSocketHelper::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $socketHelperMock
+            ->expects($this->any())
+            ->method('isResource')
+            ->willReturn(true)
+        ;
+
+        $socketHelperMock
+            ->expects($this->any())
+            ->method('getResponseCode')
+            ->willReturnOnConsecutiveCalls(220, 250, 250, 550)
+        ;
+
+        $validation = new MailboxCheckValidation($socketHelperMock, 'test@validation.email');
+        $validation->isValid('failure@validation.email', new EmailLexer());
+        $this->assertEquals(new IllegalMailbox(550), $validation->getError());
+    }
+}