Mail: Revert Set sender address by default.

This reverts [61010]. Setting the sender address by default has shown to reduce deliverability for emails for sites that were working correctly in 6.8 and before. As reduced deliverability can harm IP reputation which means it's not just the single WordPress install that is harmed, [61010] is being reverted out of an abundance of caution.

Follow up to [61010].

Props jorbin, dmsnell, SirLouen, wildworks, desrosj, siliconforks, digitalblanket, studiomondiale, zoe20, Monarobase, amanandhishoe,
Fixes #64368.See #49687.



git-svn-id: https://develop.svn.wordpress.org/trunk@61537 602fd350-edb4-49c9-b593-d223f7449a82

Author: aaronjorbin

src/wp-includes/pluggable.php

@@ -446,7 +446,7 @@ 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 );
 	}
 
 	/**