Here at Rotterdam Community Solutions we developed a full featured Newsletter portlet for Liferay >6.0. Please have look at the following url, download and test our opensource portlet and tell us what you think.
For updates, news announcements and future opensource contributions to Liferay, you can checkout our website www.rotterdam-cs.com. If you would like to collaborate or be part of our team as a freelance Liferay developer, please send us your resume through the website's contact form.
Hope this helps!