See the Kanmail documentation for help using Kanmail.
If you've misplaced your license key please email email@example.com from the purchase email and we'll be able to help.
Errors will appear at the top of the window. In the main view they appear top left, near the logo. In other windows (settings, contacts) they will appear along the top bar. Hovering over the exclamation icon will overlay more detailed error information. Please include this when creating issues.