MailClark - The Slack bot for external communications
Front - The platform for exceptional customer service at scale.
Alert.email - Get your important emails delivered to a Slack channel
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
PigeonBot - Send emails via Slack with the /email command
Missive - Team communication app now supporting FB, Twitter & SMS