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
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
SharedInbox.co - Shared inbox and help desk built on Slack
DuoCircle - DuoCircle provides enterprise spam filtering and email management solutions.