<?php $attachments = array( WP_CONTENT_DIR . '/uploads/file_to_attach.zip' ); $headers[] = 'From: My Name <myname@example.com>'; $headers[] = "Content-type: text/html" ; wp_mail('test@example.org', 'subject', 'message', $headers, $attachments ); ?>
ref: http://codex.wordpress.org/Function_Reference/wp_mail