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

Mon Jul 14 15:13:41 UTC 2025

#15448: wp_mail() sets Content-Type header twice for multipart emails
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 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                         |
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Comment (by tusharbharti):

 == Test Report
 === Description
 This report validates whether the indicated patch works as expected.

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

 === 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 138.0.0.0
 - OS: macOS
 - Theme: Twenty Twenty-Five 1.3
 - MU Plugins: None activated
 - Plugins:
   * Manual Multipart Email Debug 1.1
   * Test Reports 1.2.0

 === Actual Results
 1.  ✅ Patch is working properly and we can send multipart data via
 `$body` array

 === Supplemental Artifacts
 ==== Code
 A sample plugin to test the new patch
 {{{
 <?php
 /*
 Plugin Name: Manual Multipart Email Debug (Array Body)
 Description: Debug plugin to send multipart email using array body. Adds
 button in Tools page.
 Version: 1.2
 */

 add_action('admin_menu', function() {
     add_management_page(
         'Manual Multipart Email',
         'Manual Multipart Email',
         'manage_options',
         'manual-multipart-email',
         'manual_multipart_email_page'
     );
 });

 function manual_multipart_email_page() {
     if (!current_user_can('manage_options')) {
         return;
     }

     if (isset($_POST['manual_multipart_send_email'])) {
         $to = get_option('admin_email');
         $subject = 'Reproduce Original Issue (Array Body Method)';

         $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: Manual Multipart <manual at example.com>',
         );

         $sent = wp_mail($to, $subject, $body, $headers);

         if ($sent) {
             echo '<div class="notice notice-success"><p>Email sent
 successfully to admin email (' . esc_html($to) . ').</p></div>';
         } else {
             echo '<div class="notice notice-error"><p>Error sending array
 body email.</p></div>';
         }
     }
     ?>
     <div class="wrap">
         <h1>Manual Multipart Email Debug (Array Body)</h1>
         <form method="post">
             <?php submit_button('Send Test Email', 'primary',
 'manual_multipart_send_email'); ?>
         </form>
     </div>
     <?php
 }

 }}}

 ==== Results
 [[Image(https://i.ibb.co/PZKYRJ37/image.png)]]
 [[Image(https://i.ibb.co/7Npk6zvQ/image.png)]]

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/15448#comment:83>
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