Trello is a great project management tool that makes collaboration easy. Airmail has integration with Trello.
How to enable Trello integration ?
In Airmail, Please go to Preferences > Services > Trello > Link Trello
How to send a message to Trello?
Select a message > Right Click > Send to > Send to Trello. You can also select a message and press 'Z' for the shortcut of Send To.