MailChimp - MailChimp is the best way to design, send, and share email newsletters.
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
Campaign Monitor - Email marketing software built for designers and their clients to run successful email campaigns.
MailClark - The Slack bot for external communications
Constant Contact - Constant Contact offers email marketing, social media marketing, online survey, event marketing, digital storefronts, and local deals tools.
Hiver - Manage Customer Support, Sales and Projects right from your Gmail inbox. Collaborate with Shared Labels, Shared Contacts, email notes, email reminders and email templates