This is a subclass derived from SMTP that connects over an SSL
encrypted socket (to use this class you need a socket module that was
compiled with SSL support). If host is not specified, '' (the local
host) is used. If port is omitted, the standard SMTP-over-SSL port
(465) is used. local_hostname and source_address have the same meaning
as they do in the SMTP class. context also optional, can contain a
SSLContext.