Send Email Messages from Gmail to Slack Channel

The Google Apps Script, courtesy @andrewwilson, uses incoming webhooks to post email messages from your Gmail mailbox into Slack channel. The email body is extracted using the GmailApp service and posted to Slack through an HTTP request with a JSON payload. You need to create a ToSlack gmail label and apply this label to message that you wish to post to your Slack channel.

A time-based trigger may also be added for sending labeled message from Gmail to Slack in near real-time.