[wp-trac] [WordPress Trac] #15448: wp_mail() sets Content-Type header twice for multipart emails

Mon Jul 14 15:11:05 UTC 2025

#15448: wp_mail() sets Content-Type header twice for multipart emails
-------------------------------------------------+-------------------------
 Reporter:  rmccue                               |       Owner:
                                                 |  SergeyBiryukov
     Type:  feature request                      |      Status:  reviewing
 Priority:  normal                               |   Milestone:  Future
                                                 |  Release
Component:  Mail                                 |     Version:
 Severity:  normal                               |  Resolution:
 Keywords:  has-patch has-unit-tests has-test-   |     Focuses:
  info reported-upstream                         |
-------------------------------------------------+-------------------------

Comment (by lakshyajeet):

 == Test Report
 === Description
 This report validates whether the patch correctly addresses the
 `wp_mail()` multipart email functionality by introducing the a array-based
 `$message` parameter for native multipart sending.

 Patch tested: https://github.com/WordPress/wordpress-
 develop/pull/9063.patch

 === Environment
 - WordPress: 6.9-alpha-60093-src
 - PHP: 8.2.29
 - Server: nginx/1.29.0
 - Database: mysqli (Server: 8.4.5 / Client: mysqlnd 8.2.29)
 - Browser: Chrome 137.0.0.0
 - OS: macOS
 - Theme: Twenty Twenty-Five 1.3
 - MU Plugins: None activated
 - Plugins:
   * Test Reports 1.2.0

 === Actual Results
 1.  ✅ The report confirms the patch works correctly.

 === Additional Notes
 - Snippets used for testing

  - Manually sending a multipart mail.
 {{{#!php
 <?php
 $subject = 'Reproduce Original Issue (Manual Multipart Header)';
 $body = '--TestBoundary_Manual
 Content-Type: text/plain; charset=UTF-8

 Hello world! This is plain text from manual multipart.

 --TestBoundary_Manual
 Content-Type: text/html; charset=UTF-8

<html><body>Hello world! This is HTML from manual
 multipart.</body></html>

 --TestBoundary_Manual--';
 $headers = array(
 'MIME-Version: 1.0',
 'From: Manual Multipart <manual at example.com>',
 'Content-Type: multipart/alternative; boundary="TestBoundary_Manual"'
 );

 $sent = wp_mail($to, $subject, $body, $headers);
 if (!$sent) {
         $error = 'Error reproducing original issue email';
 }
 }}}

  - Received Mail
 {{{
 Content-Type: multipart/alternative; charset=
 Date: Mon, 14 Jul 2025 14:49:29 +0000
 From: Manual Multipart <manual at example.com>
 MIME-Version: 1.0
 Message-ID: <oNS5dFXICClL5kOA6XelQAaXByjYDMKXtJHJRkoyKBk at localhost>
 Received: from localhost by mailhog.example (MailHog)
           id YhfTbmw69cKDkxtZsPkpYTt7UfGrH5159XlngKPLU7g=@mailhog.example;
 Mon, 14 Jul 2025 14:49:29 +0000
 Return-Path: <manual at example.com>
 Subject: Reproduce Original Issue (Manual Multipart Header)
 To: test at example.com
 X-Mailer: PHPMailer 6.9.3 (https://github.com/PHPMailer/PHPMailer)

 --TestBoundary_Manual
 Content-Type: text/plain; charset=UTF-8

 Hello world! This is plain text from manual multipart.

 --TestBoundary_Manual
 Content-Type: text/html; charset=UTF-8

<html><body>Hello world! This is HTML from manual
 multipart.</body></html>

 --TestBoundary_Manual--
 }}}

  - Using the new feature `$message` as an array.
 {{{#!php
 <?php
 $subject = 'Test Patch';
 $body = array(
     'text/plain' => 'Hello world! This is plain text from array body.',
     'text/html'  => '<html><body><p>Hello world! This is
 <strong>HTML</strong> from array body.</p></body></html>'
 );
 $headers = array(
     'From: Patch Tester <patch at example.com>',
 );
 $sent = wp_mail($to, $subject, $body, $headers);
 if (!$sent) {
     $error = 'Error sending patch-tested array email';
 }
 }}}

  - Received mail
 {{{
 Content-Transfer-Encoding: 8bit
 Content-Type: multipart/alternative;
 boundary="b1=_2Y7MTiqKWSHhSj2x8qM1RMRWPivHf8MKoMNdrHYeKDE"
 Date: Mon, 14 Jul 2025 14:49:27 +0000
 From: Patch Tester <patch at example.com>
 MIME-Version: 1.0
 Message-ID: <2Y7MTiqKWSHhSj2x8qM1RMRWPivHf8MKoMNdrHYeKDE at localhost>
 Received: from localhost by mailhog.example (MailHog)
           id knwaRMzFmUCibRtxpzIqTYYq2XnfkSQ2C6GG7LRBat8=@mailhog.example;
 Mon, 14 Jul 2025 14:49:27 +0000
 Return-Path: <patch at example.com>
 Subject: Test Patch
 To: test at example.com
 X-Mailer: PHPMailer 6.9.3 (https://github.com/PHPMailer/PHPMailer)

 --b1=_2Y7MTiqKWSHhSj2x8qM1RMRWPivHf8MKoMNdrHYeKDE
 Content-Type: text/plain; charset=us-ascii

 Hello world! This is plain text from array body.

 --b1=_2Y7MTiqKWSHhSj2x8qM1RMRWPivHf8MKoMNdrHYeKDE
 Content-Type: text/html; charset=us-ascii

<html><body>Hello world! This is HTML from array
 body.</body></html>

 --b1=_2Y7MTiqKWSHhSj2x8qM1RMRWPivHf8MKoMNdrHYeKDE--
 }}}

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/15448#comment:81>
WordPress Trac <https://core.trac.wordpress.org/>
WordPress publishing platform