Takes POST data (email and optional next fields), submitting the email field to the newsletter provider for subscription to a mailing list, and redirecting the user to the value of next (this can also be provided in the querystring), or the homepage if no follow-on URL is supplied, with a message in the django.contrib.messages queue to let them know it was successful.

If the email address is invalid or the subscription process was unsuccessful, the user is redirected to the follow-on URL and a message placed in the django.contrib.messages queue letting them know what the issue was.