Code
T0020 no-mailer
mail.send was used where a message would be sent, and the app has no mailer.
Details
An app has a mailer when its project states mail with the secret that holds the address of its mail server, or when a program connected a Mailer of its own. In the mode development a message is written to the log and not sent, so this code is not raised there unless the app was started with tent dev --mail.
The fix
State mail: { from, send } in project, with the secret that holds the address of the mail server, or connect a Mailer.