send mail using smtp gateway that requires SSL

Hi..

I just downloaded postcast smtp server.
My requirement is to collect outgoing mails and send it through our
email provider that requires SSL on outgoing emails.
Postcast smtp server has gateways but cannot be used to send one
through an smtp server that requires SSL.
An error msg saying please use STARTTLS first comes up.

Please do suggest a smtp software like the postcast server that can
send mails through smtp server that require SSL.

Thanks