Ticket #37736: 37736.diff

src/wp-includes/pluggable.php

@@ -349 +349 @@
          */
         $from_name = apply_filters( 'wp_mail_from_name', $from_name );
 
-        $phpmailer->setFrom( $from_email, $from_name );
+        $phpmailer->setFrom( $from_email, $from_name, false );
 
         // Set destination addresses
         if ( !is_array( $to ) )

tests/phpunit/tests/mail.php

@@ -342 +342 @@
                         $this->assertEquals( $expected[ $header ], array_pop( $target_headers ) );
                 }
         }
+
+        /**
+         * Test that the Sender field in the SMTP envelope is not set by Core
+         *
+         * 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 37736
+         */
+        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->assertEquals( '', $mailer->Sender );
+        }
 }