mypmpro-use-plaintext-email-header.php

<?php //do not copy

/**
 * This recipe removes the HTML content type and adds a plain text content type for all PMPro emails
 * 
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function my_pmpro_email_headers( $headers, $email ) {

	$new_headers = array();

	foreach( $headers as $key => $header ) {
		//Only use the headers that don't reference the content type
		if ( strpos( $header, "text/html" ) === false ) {
			$new_headers[] = $header;
		}

	}

	//Set to plain text
	$new_headers[] = "Content-Type: text/plain";

	return $new_headers;
}
add_filter( "pmpro_email_headers", "my_pmpro_email_headers", 10, 2 );