The email trigger allows you to trigger a workflow by sending an email.
The email address of your workflow will be trigger+[ID]@traymail.io where [ID] is the routing id of your workflow. To find the routing ID of your workflow, you need to click the settings button in the top left and take a look at the "Public URL".
In this screenshot the Public URL is https://62be1fdf-ea16-4736-b45f-4a8362486b83.trayapp.io and the routing ID is 62be1fdf-ea16-4736-b45f-4a8362486b83, therefore the trigger email address would be firstname.lastname@example.org!
You can even send attachments in an email and they will be available as file objects with expiring URLs to use in other connectors.