Affects Version/s: None
Fix Version/s: 1.3
The API offers two categories of settings for the configuration of SSL/TLS: setSSL and setTLS (and respective associated methods).
The names are quite misleading, as this doesn't really oppose SSL and TLS. A number of e-mail applications make this mistake, but "TLS" is used here to mean "using STARTTLS" and "SSL" is used here to mean "SSL or TLS, upon connection".
The difference is that:
- With "SSL" (as incorrectly named here), the SMTP client connects to the SMTP server on a dedicated port and starts the SSL/TLS handshake upon connection. This is then followed by "normal" SMTP traffic on this SSL/TLS layer.
- With "TLS" (as incorrectly named here), the SMTP client connects to the SMTP server on the same port as it would do for plain-text SMTP, exchanges a few SMTP commands, including STARTTLS (RFC 3207), and then starts an SSL/TLS handshake to upgrade to a secure channel.
This is not so much a difference between SSL and TLS, but rather a difference regarding when the connection is turned into a secure one.
The difference between SSLv3 and TLS 1.0 is mostly a version difference, where SSLv3 is the predecessor of TLS 1.0.
You can have an TLS 1.0+ upon connection, using the "SSL" setting, without using STARTTLS (it's a version configuration up to the SSLEngine or SSLSocketFactory).
Similarly, although it's not written in the specification, some servers seem to accept an SSLv3 handshake (instead of its successor version: TLS 1.0) after STARTTLS.
I'd suggest deprecating setSSL and setTLS and replacing them with setOnConnectSSL and setStartTLS (or similar), respectively.