The granddaddy of secure SMTP SSL Mail Relaying is Pobox and for over a decade I have been in love with their simple, robust and reliable service. Pobox gives you a “lifetime” email and website address.
They also offer mail bomb protection from Spammers and you can invoke a powerful set of filters that will allow you to better manage your mail. My favorite part of Pobox.com is their secure mail relay service. You can use their servers to send mail from anywhere. I find the Pobox mail servers are faster and more reliable than any other major or minor ISP mail server I have used.
No only does Pobox.com offer a secure SMTP server; they also provide SSL support for their SMTP server with several ways to configure port usage in case some of your mail ports are blocked by your work or ISP firewall. Being able to send SSL secure email and to know it will get to the person you want it to reach is a singular comfort and a joy in the wild world of the wicked web.