It is true that if you connect to the email server via SSL (actually, using the SMTPS protocol) nobody can peek into your email… until they reach the server.
Usually, email servers connect to each other via SMTP, without encryption. And this is the problem as the connection between them is plain text and anybody can read the content.
The only secure way to make sure that only you and the intended recipient is to encrypt the email. Of course, you need to encrypt the email using PKI so that the recipient can have the possibility to decrypt it.
All these and many more topics are in the free eBook "Improve your security" available here: www.improve-your-security.org.