is there a help page with all syntax available?
in order to add a due date to a task added via email, please use the <date> tag either within the subject or the body of the email.
For example: <date tomorrow> or <date every day>
You can read detailed information about what syntax you can use with this feature by accessing a project and clicking on the small envelope icon in the top-right corner or your task list. The information can be found below the unique email address assigned to this particular project.