MailClark - The Slack bot for external communications
PigeonBot - Send emails via Slack with the /email command
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
Clubble.io - Answer emails via Slack.
SharedInbox.co - Shared inbox and help desk built on Slack
Helpwise - Shared inbox for your team email addresses