Sidemail - The simplest way to send transactional emails. Sidemail makes sending transactional emails trivial, it's perfect for side projects, MVPs or the next big thing.
Email Architect - All-in-one system to write, manage and organize email
Mailivery - Reach the Inbox, not the spam folder.
KanbanMail - A Kanban board for your emails.
Postal - Open source mail delivery platform, alternative to Mailgun or Sendgrid
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.