diff --git a/src/wp-includes/pluggable.php b/src/wp-includes/pluggable.php
index c614ac0ed6..b2ed4642c5 100644
--- a/src/wp-includes/pluggable.php
+++ b/src/wp-includes/pluggable.php
@@ -216,6 +216,10 @@ if ( ! function_exists( 'wp_mail' ) ) :
 			require_once ABSPATH . WPINC . '/PHPMailer/SMTP.php';
 			require_once ABSPATH . WPINC . '/PHPMailer/Exception.php';
 			$phpmailer = new PHPMailer\PHPMailer\PHPMailer( true );
+
+			$phpmailer::$validator = static function ( $email ) {
+				return (bool) is_email( $email );
+			};
 		}
 
 		// Headers.
diff --git a/tests/phpunit/includes/mock-mailer.php b/tests/phpunit/includes/mock-mailer.php
index edc36b9ec6..e5e3d98fa2 100644
--- a/tests/phpunit/includes/mock-mailer.php
+++ b/tests/phpunit/includes/mock-mailer.php
@@ -96,7 +96,12 @@ function tests_retrieve_phpmailer_instance() {
 function reset_phpmailer_instance() {
 	$mailer = tests_retrieve_phpmailer_instance();
 	if ( $mailer ) {
-		$GLOBALS['phpmailer'] = new MockPHPMailer( true );
+		$mailer             = new MockPHPMailer( true );
+		$mailer::$validator = static function ( $email ) {
+			return (bool) is_email( $email );
+		};
+
+		$GLOBALS['phpmailer'] = $mailer;
 		return true;
 	}
 
diff --git a/tests/phpunit/tests/mail.php b/tests/phpunit/tests/mail.php
index d24d5e831a..f520e1e5a0 100644
--- a/tests/phpunit/tests/mail.php
+++ b/tests/phpunit/tests/mail.php
@@ -407,4 +407,12 @@ class Tests_Mail extends WP_UnitTestCase {
 		$this->assertEquals( 'wp_mail_failed', $call_args[0]->get_error_code() );
 		$this->assertEquals( $expected_error_data, $call_args[0]->get_error_data() );
 	}
+
+	/**
+	 * @ticket 50720
+	 */
+	function test_phpmailer_validator() {
+		$phpmailer = $GLOBALS['phpmailer'];
+		$this->assertTrue( $phpmailer->validateAddress( 'foo@192.168.1.1' ), 'Assert PHPMailer accepts IP address email addresses' );
+	}
 }