diff --git a/composer.json b/composer.json
index b683a16..eba75d0 100644
--- a/composer.json
+++ b/composer.json
@@ -3,7 +3,8 @@
     "description": "Remove aliases from email and get primary email account",
     "type": "library",
     "require": {
-        "php": "^7.0.0"
+        "php": "^7.0.0",
+        "ext-mbstring": "*"
     },
     "require-dev": {
         "phpunit/phpunit": "6.5.14",
diff --git a/src/Emails/Email.php b/src/Emails/Email.php
index f94b955..cab0134 100644
--- a/src/Emails/Email.php
+++ b/src/Emails/Email.php
@@ -8,19 +8,25 @@ class Email implements EmailInterface
 {
     use EmailTrait;
 
-    public function __construct(string $email, bool $caseSensitive = false)
+    const PATTERN_WITH_SUPPORT_CYRILLIC = '/^[a-zA-Zа-яА-Я0-9.!#$%&\'*+\\/=?^_`{|}~-]+@[a-zA-Zа-яА-Я0-9](?:[a-zA-Zа-яА-Я0-9-]{0,61}[a-zA-Zа-яА-Я0-9])?(?:\.[a-zA-Zа-яА-Я0-9](?:[a-zA-Zа-яА-Я0-9-]{0,61}[a-zA-Zа-яА-Я0-9])?)+$/u';
+
+    public function __construct(string $email, bool $caseSensitive = false, bool $cyrillicAllowed = false)
     {
-        $this->validateEmail($email);
+        $this->validateEmail($email, $cyrillicAllowed);
         list($this->localPart, $this->domain) = explode('@', $email);
         if (!$caseSensitive) {
-            $this->localPart = strtolower($this->localPart);
+            $this->localPart = mb_strtolower($this->localPart);
         }
-        $this->domain = strtolower($this->domain);
+        $this->domain = mb_strtolower($this->domain);
     }
 
-    private function validateEmail(string $email)
+    private function validateEmail(string $email, bool $cyrillicAllowed)
     {
-        if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
+        if ($cyrillicAllowed && !preg_match(self::PATTERN_WITH_SUPPORT_CYRILLIC, $email)) {
+            throw new InvalidEmailException("Email '{$email}' is not valid!");
+        }
+
+        if (!$cyrillicAllowed && !filter_var($email, FILTER_VALIDATE_EMAIL)) {
             throw new InvalidEmailException("Email '{$email}' is not valid!");
         }
     }
diff --git a/tests/Emails/EditableEmailTest.php b/tests/Emails/EditableEmailTest.php
index 8049bd1..cf31282 100644
--- a/tests/Emails/EditableEmailTest.php
+++ b/tests/Emails/EditableEmailTest.php
@@ -127,7 +127,7 @@ class EditableEmailTest extends TestCase
         $editable = new EditableEmail($email);
         $new = $editable->lowerCaseLocalPartIf($condition);
         $this->assertSame(!$condition, $editable === $new);
-        $this->assertSame($isLowerCase, strtolower($editable->getLocalPart()) === $new->getLocalPart());
+        $this->assertSame($isLowerCase, mb_strtolower($editable->getLocalPart()) === $new->getLocalPart());
         $this->assertSame($email->getDomain(), $new->getDomain());
     }
 
diff --git a/tests/Emails/EmailTest.php b/tests/Emails/EmailTest.php
index c559de7..0939909 100644
--- a/tests/Emails/EmailTest.php
+++ b/tests/Emails/EmailTest.php
@@ -18,18 +18,20 @@ class EmailTest extends TestCase
      * @param string $localPart
      * @param string $domain
      * @param bool $caseSensitive
+     * @param bool $cyrillicAllowed
      */
     public function testConstructor(
         string $email,
         bool $expectedException,
         string $localPart = '',
         string $domain = '',
-        bool $caseSensitive = false
+        bool $caseSensitive = false,
+        bool $cyrillicAllowed = false
     ) {
         if ($expectedException) {
             $this->expectException(InvalidEmailException::class);
         }
-        $object = new Email($email, $caseSensitive);
+        $object = new Email($email, $caseSensitive, $cyrillicAllowed);
         $this->assertSame($localPart, $object->getLocalPart());
         $this->assertSame($domain, $object->getDomain());
     }
@@ -41,6 +43,13 @@ class EmailTest extends TestCase
             ['.johndoe@example.com', true],
             ['Jane.Doe@Example.COM', false, 'Jane.Doe', 'example.com', true],
             ['Jane.Doe@Example.COM', false, 'jane.doe', 'example.com'],
+            // Cyrillic use
+            ['тест тест@example.com', true],
+            ['.тест@example.com', true],
+            ['Тест.Тест@Example.COM', false, 'Тест.Тест', 'example.com', true, true],
+            ['Тест.Тест@Example.COM', false, 'тест.тест', 'example.com', false, true],
+            ['Тест.Тест@Тест.РУ', false, 'Тест.Тест', 'тест.ру', true, true],
+            ['Тест.Тест@Тест.РУ', false, 'тест.тест', 'тест.ру', false, true],
         ];
     }
 }
\ No newline at end of file
diff --git a/tests/Services/MailRuTest.php b/tests/Services/MailRuTest.php
index 13dd81c..e80dc9b 100644
--- a/tests/Services/MailRuTest.php
+++ b/tests/Services/MailRuTest.php
@@ -15,10 +15,11 @@ class MailRuTest extends TestCase
      *
      * @param string $inputEmail
      * @param string $outputEmail
+     * @param bool $cyrillicAllowed
      */
-    public function testGetPrimaryEmail(string $inputEmail, string $outputEmail)
+    public function testGetPrimaryEmail(string $inputEmail, string $outputEmail, bool $cyrillicAllowed = false)
     {
-        $this->assertEquals($outputEmail, (new MailRu())->getPrimaryEmail(new Email($inputEmail)));
+        $this->assertEquals($outputEmail, (new MailRu())->getPrimaryEmail(new Email($inputEmail, false, $cyrillicAllowed)));
     }
 
     public function providerGetPrimaryEmail() : array
@@ -27,6 +28,10 @@ class MailRuTest extends TestCase
             ['foobar@MAIL.RU', 'foobar@mail.ru'],
             ['fOObar@MaiL.Ru', 'foobar@mail.ru'],
             ['foobar+alias@mail.ru', 'foobar@mail.ru'],
+            // Cyrillic use
+            ['иванов@MAIL.RU', 'иванов@mail.ru', true],
+            ['иванОВ@MaiL.Ru', 'иванов@mail.ru', true],
+            ['иванов+alias@mail.ru', 'иванов@mail.ru', true],
         ];
     }
 
diff --git a/tests/Services/YandexRuTest.php b/tests/Services/YandexRuTest.php
index 797f7fd..9a88120 100644
--- a/tests/Services/YandexRuTest.php
+++ b/tests/Services/YandexRuTest.php
@@ -15,10 +15,11 @@ class YandexRuTest extends TestCase
      *
      * @param string $inputEmail
      * @param string $outputEmail
+     * @param bool $cyrillicAllowed
      */
-    public function testGetPrimaryEmail(string $inputEmail, string $outputEmail)
+    public function testGetPrimaryEmail(string $inputEmail, string $outputEmail, bool $cyrillicAllowed = false)
     {
-        $this->assertEquals($outputEmail, (new YandexRu())->getPrimaryEmail(new Email($inputEmail)));
+        $this->assertEquals($outputEmail, (new YandexRu())->getPrimaryEmail(new Email($inputEmail, false, $cyrillicAllowed)));
     }
 
     public function providerGetPrimaryEmail() : array
@@ -33,6 +34,16 @@ class YandexRuTest extends TestCase
             ['foobar@yandex.by', 'foobar@yandex.ru'],
             ['foobar@yandex.kz', 'foobar@yandex.ru'],
             ['foobar@yandex.ua', 'foobar@yandex.ru'],
+            // Cyrillic use
+            ['иванов@YANDEX.RU', 'иванов@yandex.ru', true],
+            ['иванОВ@YAndEX.ru', 'иванов@yandex.ru', true],
+            ['иванов+alias@yandex.ru', 'иванов@yandex.ru', true],
+            ['ИвановИван@ya.ru', 'ивановиван@yandex.ru', true],
+            ['Иванов.Иван@ya.ru', 'иванов-иван@yandex.ru', true],
+            ['иванов@yandex.com', 'иванов@yandex.ru', true],
+            ['иванов@yandex.by', 'иванов@yandex.ru', true],
+            ['иванов@yandex.kz', 'иванов@yandex.ru', true],
+            ['иванов@yandex.ua', 'иванов@yandex.ru', true],
         ];
     }