danieliser/custom-email-template.php

## custom-email-template.php

<?php

function get_custom_email_template() {
	ob_start();
	include __DIR__ . '/index.php';
	$content = ob_get_clean();
	ob_end_clean();
	return $content;
}

function custom_wp_mail_atts( $atts ) {

	$headers = [
		'Content-type: text/html; charset=UTF-8',
	];

	$template_tags = [
		'[title]'     => $atts['subject'],
		'[subject]'   => $atts['subject'],
		'[content]'   => $atts['message'],
		'[copyright]' => sprintf( "© %d %s, All rights reserved", date( 'Y' ), get_bloginfo( 'name' ) ),
	];

	$content = get_custom_email_template();

	foreach( $template_tags as $tag => $value ) {
		$content = str_replace( array_keys( $template_tags ), array_values( $template_tags ), $content );
	}

	$atts["message"] = $content;
	$atts['headers'] = is_array( $atts['headers'] ) ?
		array_merge( $atts['headers'], $headers ) :
		$headers;

	return $atts;
}

add_filter( 'wp_mail', 'custom_wp_mail_atts', 10 );

function custom_email_template_attachments( &$phpmailer) {
	$template_images = [
		'logo' => 'logo.png',
		'shadow' => 'shadow.png',
	];

	$used_tags =

	$phpmailer->SMTPKeepAlive = true;

	foreach( $template_images as $uid => $file ) {
		if ( is_file( __DIR__ . '/img/' . $file ) ) {
			$phpmailer->AddEmbeddedImage(
				__DIR__ . '/img/' . $file,
				$uid,
				$file
			);
		}
	}

}

add_action( 'phpmailer_init', 'custom_email_template_attachments' );


## template.php
<!DOCTYPE html>
<html lang="en" xmlns="http://www.w3.org/1999/xhtml" xmlns:o="urn:schemas-microsoft-com:office:office">
    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width,initial-scale=1">
        <meta name="x-apple-disable-message-reformatting">
        <title>[title]</title>
        <!--[if mso]>
        <noscript>
            <xml>
                <o:OfficeDocumentSettings>
                    <o:PixelsPerInch>96</o:PixelsPerInch>
                </o:OfficeDocumentSettings>
            </xml>
        </noscript>
        <![endif]-->
        <style>
            table, td, div, h1, p {font-family: Arial, sans-serif;}
        </style>
    </head>
    <body style="margin:0;padding:0;">
        <table role="presentation" style="width:100%;border-collapse:collapse;border:0;border-spacing:0;background:#ffffff;">
            <tr>
                <td align="center" style="padding:0;">
                    <img src="cid:logo" width="300" />
                    [content]
                    <img src="cid:shadow" width="300" />
                </td>
            </tr>
        </table>
    </body>
</html>

	<?php

	function get_custom_email_template() {
	ob_start();
	include __DIR__ . '/index.php';
	$content = ob_get_clean();
	ob_end_clean();
	return $content;
	}

	function custom_wp_mail_atts( $atts ) {

	$headers = [
	'Content-type: text/html; charset=UTF-8',
	];

	$template_tags = [
	'[title]' => $atts['subject'],
	'[subject]' => $atts['subject'],
	'[content]' => $atts['message'],
	'[copyright]' => sprintf( "© %d %s, All rights reserved", date( 'Y' ), get_bloginfo( 'name' ) ),
	];

	$content = get_custom_email_template();

	foreach( $template_tags as $tag => $value ) {
	$content = str_replace( array_keys( $template_tags ), array_values( $template_tags ), $content );
	}

	$atts["message"] = $content;
	$atts['headers'] = is_array( $atts['headers'] ) ?
	array_merge( $atts['headers'], $headers ) :
	$headers;

	return $atts;
	}

	add_filter( 'wp_mail', 'custom_wp_mail_atts', 10 );

	function custom_email_template_attachments( &$phpmailer) {
	$template_images = [
	'logo' => 'logo.png',
	'shadow' => 'shadow.png',
	];

	$used_tags =

	$phpmailer->SMTPKeepAlive = true;

	foreach( $template_images as $uid => $file ) {
	if ( is_file( __DIR__ . '/img/' . $file ) ) {
	$phpmailer->AddEmbeddedImage(
	__DIR__ . '/img/' . $file,
	$uid,
	$file
	);
	}
	}

	}

	add_action( 'phpmailer_init', 'custom_email_template_attachments' );
	<!DOCTYPE html>
	<html lang="en" xmlns="http://www.w3.org/1999/xhtml" xmlns:o="urn:schemas-microsoft-com:office:office">
	<head>
	<meta charset="UTF-8">
	<meta name="viewport" content="width=device-width,initial-scale=1">
	<meta name="x-apple-disable-message-reformatting">
	<title>[title]</title>
	<!--[if mso]>
	<noscript>
	<xml>
	<o:OfficeDocumentSettings>
	<o:PixelsPerInch>96</o:PixelsPerInch>
	</o:OfficeDocumentSettings>
	</xml>
	</noscript>
	<![endif]-->
	<style>
	table, td, div, h1, p {font-family: Arial, sans-serif;}
	</style>
	</head>
	<body style="margin:0;padding:0;">
	<table role="presentation" style="width:100%;border-collapse:collapse;border:0;border-spacing:0;background:#ffffff;">
	<tr>
	<td align="center" style="padding:0;">
	<img src="cid:logo" width="300" />
	[content]
	<img src="cid:shadow" width="300" />
	</td>
	</tr>
	</table>
	</body>
	</html>