In the code, it looks like setting "Use TLS" to true actually makes the component to use the STARTTLS command to negotiate secure TLS or SSL connection (after first connecting insecurely). "Use STARTTLS" instead of "Use TLS" looks more precise to me.
Both "Use STARTTLS" and "Use SSL" set to true doesn't make much sense. "Use SSL" means that secure connection is used right fro the beginning, using the STARTTLS command to establish new secure connection is useless. Maybe checkConfig could warn about this (using combobox instead of the checkboxes would be better, but backwards incompatible).
Another issue to think about is that, currently, if user sets the STARTTLS to be used, but SMTP server for whatever reason refuses to initiate secure connection after the STARTTLS client command, the communication continues unencrypted. That's because we do not set the mail.smtp.starttls.required connection property to true. Maybe we should do so.