WP plugin for building and sending newsletters using mailgun
Warning: there is some debug code in notifyMailgunResponse() that will send me an email each time you send an email. I'll be removing this eventually but if this warning is still here you should remove it yourself, if you are worried about it.
You will need to reapply permalinks after plugin activation (I know).
You can copy archive-newsletter.php to your theme and modify to cusomize the archive page. Or skip it and get archive defaults.