Revert [61010]

src/wp-includes/pluggable.php

@@ -444,7 +444,7 @@ function wp_mail( $to, $subject, $message, $headers = '', $attachments = array()
 		$from_name = apply_filters( 'wp_mail_from_name', $from_name );
 
 		try {
-			$phpmailer->setFrom( $from_email, $from_name );
+			$phpmailer->setFrom( $from_email, $from_name, false );
 		} catch ( PHPMailer\PHPMailer\Exception $e ) {
 			$mail_error_data                             = compact( 'to', 'subject', 'message', 'headers', 'attachments' );
 			$mail_error_data['phpmailer_exception_code'] = $e->getCode();

tests/phpunit/tests/pluggable/wpMail.php

@@ -411,18 +411,21 @@ public function test_wp_mail_addresses_arent_encoded() {
 	}
 
 	/**
-	 * Test that the Sender field in the SMTP envelope is set by Core.
+	 * Test that the Sender field in the SMTP envelope is not set by Core.
 	 *
-	 * A missing Sender field can lead to messages failing DMARC SPF checks.
+	 * Correctly setting the Sender requires knowledge that is not available
+	 * to Core. An incorrect value will often lead to messages being rejected
+	 * by the receiving MTA, so it's the admin's responsibility to
+	 * set it correctly.
 	 *
-	 * @ticket 49687
+	 * @ticket 37736
 	 */
-	public function test_wp_mail_sender_set() {
-		wp_mail( 'user@example.org', 'Testing the Sender field', 'The Sender field should have been set.' );
+	public function test_wp_mail_sender_not_set() {
+		wp_mail( 'user@example.org', 'Testing the Sender field', 'The Sender field should not have been set.' );
 
 		$mailer = tests_retrieve_phpmailer_instance();
 
-		$this->assertSame( 'wordpress@example.org', $mailer->Sender );
+		$this->assertSame( '', $mailer->Sender );
 	}
 
 	/**