PopcornNotify - Send simple emails and text messages from one API
MailClark - The Slack bot for external communications
MailerSend - Better transactional emails for teams.
iDoneThis - iDoneThis The fun, easy way to get stuff done. Every day we’ll email your team to ask, “What’d you get done today?” Just reply to our email. The next day, everyone gets an email with the team's accomplishments
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