The "email-send-method" setting:

Determine the method used to send email.  Allowed values are
"off", "pipe", "dir", "db", and "stdout".  The "off" value means
no email is ever sent.  The "pipe" value means email messages are
piped into a command determined by the email-send-command setting.
The "dir" value means emails are written to individual files in a
directory determined by the email-send-dir setting.  The "db" value
means that emails are added to an SQLite database named by the
email-send-db setting.  The "stdout" value writes email text to
standard output, for debugging.