Postbox should use SSL or TLS for new accounts by default

Postbox should use SSL or TLS for new accounts by default and only configure unencrypted connections if SSL or TLS really aren't available. The "TLS, if available" option should be removed as it is a security risk (it allows man-in-the-middle attacks).

Thunderbird 3 seems to get this right, use should include those changes in Postbox.