MailerSend - Better transactional emails for teams.
MailClark - The Slack bot for external communications
Mailjet - All-in-one email service provider that provides maximum insight and deliverability results for both marketing and transactional emails.
PigeonBot - Send emails via Slack with the /email command
Inbox Ignite - Prevent your emails from going into spam
Good Email Copy - Email copy from great companies.