Dovecot

It is a free and open-source mail transfer agent that routes and delivers electronic mail. It is Wietse Venema's mail server that started life at IBM research as an alternative to the widely-used Sendmail program. Now at Google, Wietse continues to support it.

It adds scheduled sending and the easiest, most integrated email reminders to Gmail, helping you reach Inbox Zero.

250ok is an email deliverability tools company that produces a Software‐as‐a‐Service (“SaaS”) platform to monitor and measure the deliverability of email networks. These networks consist of companies sending various forms of messages including marketing, transactional, share, and others from various platforms.

It helps build lasting business relationships, right from your inbox. A sales engagement platform designed for sales professionals and account managers.

It is an all-in-one tool for email deliverability to make your Email Channel Reliable. It raises your sender reputation by interacting with real people in any language and helps you to hit the inbox of your prospect. Full automation.

Pinpoint email issues before you hit "send". Secure your emails from malicious actors and ensure your email delivery to the inbox.

Your transactional email should NOT trigger spam or marketing filters. Flute Mail plugs into your existing API provider to properly isolate segments, boost inbox rates, and safely store your transactional email data.

It is an easy way to manage your outgoing emails from your apps. From creating and sending your emails to monitoring and managing their stats, you can do really useful things with it without worried about time zone disaverage.

It helps new brands and startups build an audience while they focus on building a product

It offers a simple REST-based JSON API enabling you to thoroughly check and verify email addresses right at the point of entry into your system.

It is an advanced MTA built to handle the most critical reliability, performance, security, and deliverability requirements.

It is an all-in-one email deliverability platform to supercharge your email performance. Locate, solve, prevent email deliverability pitfalls, and become a credible sender for any ESP provider.

It is an Email Tracking for Gmail and GSuite, adds the double check marks to your mail if it is read by recipient (Just like WhatsApp), Receives real-time pop-ups notification on your desktop when your emails are opened.