THZ on "[Plugin: WP Mail SMTP] Test Message Sent The result was: bool(false)"

Hello
I'm having the same problem, installed, but doesn't work.

all mails via smtp
-set return path checked
-smtp host - smtp.mydomain.com
-smtp port - 587
-ssl encryption
-not using smtp authentication [and also tried: use smtp authentication]

Error: SMTP -> ERROR: Failed to connect to server: (0)

UPDATE: Already solved - had to use TLS instead of SSL !