Email: Error ‘smtpHost’ is empty

In case the execution of a batch (a server-side JS action) fails when trying to send an email with a message errore like the following:

it means that the SMPT host parameter has not been set.
That parameter can be defined within the Application parameters window:
It is likely that additional parameters must be defined too, related to the SMTP task: like username and password required by the SMTP server. Which parameters are needed depends on the specific SMTP server configuration.