diff --git a/composer.json b/composer.json
index f9e25e347..313230c9d 100644
--- a/composer.json
+++ b/composer.json
@@ -14,6 +14,7 @@
   ],
   "require": {
     "php": ">=5.6",
+    "egulias/email-validator": "^2.0",
     "sendgrid/php-http-client": "~3.10",
     "starkbank/ecdsa": "0.*",
     "ext-curl": "*",
diff --git a/lib/helper/Assert.php b/lib/helper/Assert.php
index f1da609a7..b823ac1d1 100644
--- a/lib/helper/Assert.php
+++ b/lib/helper/Assert.php
@@ -8,6 +8,8 @@
 
 namespace SendGrid\Helper;
 
+use Egulias\EmailValidator\EmailLexer;
+use Egulias\EmailValidator\Validation\RFCValidation;
 use SendGrid\Mail\TypeException;
 
 class Assert
@@ -47,11 +49,7 @@ public static function email($value, $property, $message = null)
     {
         static::string($value, $property, $message);
 
-        //  Define additional flags for filter_var to verify unicode characters on local part
-        //  Constant FILTER_FLAG_EMAIL_UNICODE is available since PHP 7.1
-        $flags = (defined('FILTER_FLAG_EMAIL_UNICODE')) ? FILTER_FLAG_EMAIL_UNICODE : null;
-
-        if (filter_var($value, FILTER_VALIDATE_EMAIL, $flags) === false) {
+        if ((new RFCValidation())->isValid($value, new EmailLexer()) === false) {
             $message = sprintf(
                 $message ?: '"$%s" must be a valid email address. Got: %s',
                 $property,
diff --git a/test/unit/AssertTest.php b/test/unit/AssertTest.php
index 313f325c3..4faca0c82 100644
--- a/test/unit/AssertTest.php
+++ b/test/unit/AssertTest.php
@@ -41,6 +41,14 @@ public function testEmailThrowExceptionWithDefaultMessage()
         Assert::email('test', 'test');
     }
 
+    public function testEmailThrowExceptionWithNonRFCFormatWithDefaultMessage()
+    {
+        $this->expectException(TypeException::class);
+        $this->expectExceptionMessage('"$test" must be a valid email address. Got: test');
+
+        Assert::email('test sd@test.es', 'test');
+    }
+
     public function testEmailThrowExceptionWithCustomMessage()
     {
         $this->expectException(TypeException::class);