Fix issue with smtp and STARTTLS/SMTPS

[markkrj]

Fixes #519

We used starttls by setting mail.smtp.starttls.enable=true in advanced settings. After 579c6ab it started failing.
I wen't on and checked the new code. I'm not a programmer, but I think that with this piece of code, the advanced settings that are behind this try block will never run when using plain text SMTP.

        try
        {
            if ( smtpServerType == SmtpServerType.SMTP )
            {
                return properties;
            }

I noticed also that if it was set to use START_TLS, it would also set SSL properties, which is wrong also.
It must be SSL (usually on port 465) or StartTLS (usually port 587). Never both.

As I'm not a programmer, I'm not sure that the small changes that I did are the correct approach for this issue but I tested and it worked for every scenarios that I thought would be more common as:

Plain SMTP with advanced mail.smtp.starttls.enable=true (As I was using before)
Plain SMTP with no starttls (usual no encryption, port 25, with auth).
SMTPS (with auth)
START_TLS (with auth)

Only scenarios that I didn't test are without authentication. But my patch didn't touch that.

[markkrj]

@jrivard any comments on this? Not the proper solution? I tested every scenario and it actually fixed the bug. The current implementation is wrong as:

• If using SMTP, advanced settings are not set.
• If using STARTTLS, SSL properties are also set.
  Only scenario that works with current behavior is SSL (SMTPS).