eNewsletters are emailed newsletters in a message or document that is sent out to subscribers, typically on a regular basis; daily, weekly, monthly, or quarterly.
Considerations should be put to the content being 'mobile response' and easy-to-read on smartphones as a significant majority of subscribers with read the newsletter on a smartphone.
Streamsend - Email Marketing Automation and Behavioral Targeting
Vertical Response - Email and social media marketing
Zurb - responsive email templates