Mailman - Mailman is free software for managing electronic mail discussion and e-newsletter lists.
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
Gmane - Gmane (pronounced like "mane") allows users to access and participate in e-mail-based...
MailClark - The Slack bot for external communications
MailerLite - Affordable Email Marketing Software. Get all features (Segmentation, Automation, A/B testing) for up to 1,000 subscribers & send unlimited emails for free!
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