multipart/mixed eMails for Embedded Images

Hi,

I got it working like this….

• Add a global phpmailer_init that checks if emails have this header and does the $phpmailer->addEmbeddedImage
• Add an array of cid=>file_paths in a new mail header called X-Embedded-Images
• Call wp_mail as normal

Details

X-Embedded-Images Header Setup

            $dom = new DOMDocument();
            libxml_use_internal_errors(true);
            $dom->loadHTML($email_html);
            libxml_clear_errors();
            
            $xpath = new DOMXPath($dom);

            // Find all the imgs and prepare them for CID embedding
            $images = $xpath->query('//img');
            $embedded_images = [];
            foreach ($images as $img) {
                $src = $img->getAttribute('src');
                $parsed_url = parse_url($src);
                $path = ABSPATH . substr($parsed_url['path'], strlen('/wordpress/'));
                $cid = basename($path);
                $img->setAttribute('src', 'cid:' . $cid);
                $embedded_images[] = [
                    'path' => $path,
                    'cid' => $cid
                ];
            }
            $email_html = $dom->saveHTML();

            // Store embedded images data in a custom header that survives the queue
            if ( !empty($embedded_images) ) {
                $embedded_images_data = base64_encode(serialize($embedded_images));
                $headers[] = "X-Embedded-Images: {$embedded_images_data}";
            }

phpmailer_init action is…

    add_action('phpmailer_init', 'reconstruct_embedded_images', 10);
        
    static function reconstruct_embedded_images($phpmailer) {
        // Check if this email has embedded images stored in headers
        $custom_headers = $phpmailer->getCustomHeaders();
        
        foreach ($custom_headers as $header) {
            if (strpos($header[0], 'X-Embedded-Images') === 0) {
                // Decode the embedded images data
                $embedded_data = unserialize(base64_decode($header[1]));
                
                if (is_array($embedded_data)) {
                    foreach ($embedded_data as $image) {
                        if (isset($image['path']) && isset($image['cid']) && file_exists($image['path'])) {
                            $phpmailer->addEmbeddedImage($image['path'], $image['cid']);
                        }
                    }
                }
                
                // Remove the custom header so it doesn't appear in the final email
                $phpmailer->clearCustomHeaders();
                
                // Re-add all other custom headers except the X-Embedded-Images one
                foreach ($custom_headers as $other_header) {
                    if (strpos($other_header[0], 'X-Embedded-Images') !== 0) {
                        $phpmailer->addCustomHeader($other_header[0], $other_header[1]);
                    }
                }
                
                break;
            }
        }
    }