port, use the (host, port) tuple format for the *mailhost* argument. If you
use a string, the standard SMTP port is used. If your SMTP server requires
authentication, you can specify a (username, password) tuple for the
- *credentials* argument. If *secure* is True, then the handler will attempt
- to use TLS for the email transmission.
+ *credentials* argument.
+
+ To specify the use of a secure protocol (TLS), pass in a tuple to the
+ *secure* argument. This will only be used when authentication credentials are
+ supplied. The tuple should be either an empty tuple, or a single-value tuple
+ with the name of a keyfile, or a 2-value tuple with the names of the keyfile
+ and certificate file. (This tuple is passed to the
+ :meth:`smtplib.SMTP.starttls` method.)
.. versionchanged:: 2.6
*credentials* was added.