inline images with wp_mail

Custom_Mailer.php

<?php

/*
 * Send HTML Emails with inline images
 */
class Custom_Mailer
{
    public $email_attachments = [];

    public function send($to, $subject, $body, $headers, $attachments)
    {
        /* Used by "phpmailer_init" hook to add attachments directly to PHPMailer  */
        $this->email_attachments = $attachments;

        /* Setup Before send email */
        add_action('phpmailer_init', [$this, 'add_attachments_to_php_mailer']);
        add_filter('wp_mail_content_type', [$this, 'set_content_type']);
        add_filter('wp_mail_from', [$this, 'set_wp_mail_from']);
        add_filter('wp_mail_from_name', [$this, 'wp_mail_from_name']);
        
        /* Send Email */
        $is_sent = wp_mail($to, $subject, $body, $headers);
        
        /* Cleanup after send email */
        $this->email_attachments = [];
        remove_action('phpmailer_init', [$this, 'add_attachments_to_php_mailer']);
        remove_filter('wp_mail_content_type', [$this, 'set_content_type']);
        remove_filter('wp_mail_from', [$this, 'set_wp_mail_from']);
        remove_filter('wp_mail_from_name', [$this, 'wp_mail_from_name']);

        return $is_sent;
    }

    public function add_attachments_to_php_mailer(&$phpmailer)
    {
        $phpmailer->SMTPKeepAlive=true;
        
        /* Sendgrid */
        if (defined('SENDGRID_PASSWORD')) {
            $phpmailer->IsSMTP();
            $phpmailer->Host="smtp.sendgrid.net";
            $phpmailer->Port = 587;
            $phpmailer->SMTPAuth = true;
            $phpmailer->SMTPSecure = 'tls';
            $phpmailer->Username="apikey";
            $phpmailer->Password = SENDGRID_PASSWORD;   /* api key from sendgrid */
        }

        /* Add attachments to mail */
        foreach ($this->email_attachments as $attachment) {
            if (file_exists($attachment['path'])) {
                $phpmailer->AddEmbeddedImage($attachment['path'], $attachment['cid']);
            }
        }
    }

    public function set_content_type()
    {
        return "text/html";
    }
    
    public function set_wp_mail_from($email)
    {
        //Make sure the email is from the same domain
        //as your website to avoid being marked as spam.
        return strip_tags(get_option('admin_email'));
    }

    public function wp_mail_from_name($name)
    {
        return get_bloginfo('name');
    }
}




/* Usage */

/* Set mail parameters */
$to = '[email protected]';
$subject = 'Inline Img';
$body = '<h1>Image:</h1> <img src="cid:my_img_cid"/>';
$headers = "";
$my_attachments = [
    [
        "cid" => "my_img_cid", /* used in email body */
        "path" => plugin_dir_path(__FILE__) . '/my_img.png',
    ],
];

$custom_mailer = new Custom_Mailer();
$custom_mailer->send($to, $subject, $body, $headers, $my_attachments);

messy_solution.php

<?php

global $global_attachments;
$global_attachments = [];
    
function add_attachments_to_php_mailer(&$phpmailer)
{
    /* Required */
    $phpmailer->SMTPKeepAlive=true;
    $phpmailer->ContentType = "text/html";
    $phpmailer->From = strip_tags(get_option('admin_email'));
    $phpmailer->FromName = get_bloginfo('name');

    /* Sendgrid */
    $phpmailer->IsSMTP();
    $phpmailer->Host="smtp.sendgrid.net";
    $phpmailer->Port = 587;
    $phpmailer->SMTPAuth = true;    
    $phpmailer->SMTPSecure = 'tls';
    $phpmailer->Username="apikey";
    $phpmailer->Password = '';   /* api key from sendgrid */

    /* Add attachments to mail */
    global $global_attachments;
    foreach ($global_attachments as $attachment) {
        if (file_exists($attachment['path'])) {
            $phpmailer->AddEmbeddedImage($attachment['path'], $attachment['cid']);
        }
    }
}


function send_mail($to, $subject, $body, $headers = "", $attachments = [])
{
    global $global_attachments;
    
    /* Setup before sending email */
    $global_attachments = $attachments;
    add_action('phpmailer_init', 'add_attachments_to_php_mailer');
    
    /* Send Email */
    $is_sent = wp_mail($to, $subject, $body, $headers);
    
    /* Cleanup after email is sent */
    remove_action('phpmailer_init', 'add_attachments_to_php_mailer');
    $global_attachments = [];
    
    return $is_sent;
}



/* Usage */

/* Set mail parameters */
$to = '[email protected]';
$subject = 'Inline Img';
$body = '<h1>Image:</h1> <img src="cid:my_img_cid"/>';

$attachments = [
    [
        "cid" => "my_img_cid", /* used in email body */
        "path" => plugin_dir_path(__FILE__) . '/my_img.png',
    ],
];

$is_sent = send_mail($to, $subject, $body, $headers, $attachments);

var_dump( $is_sent );