This looks like network problem. Even though it could occur due to variety of reasons, like :-
"Couldn't connect to host, port" could be caused by wrong host name, wrong port, a blocking firewall (on the server, on gateways, even on your own machine), network failure, server downtime, etc.
Can you connect to the mail server using telnet ?
Also see this FAQ for some mistakes you committed http://www.oracle.com/technetwork/java/javamail/faq/index.html#commonmistakes
Read this answer on how to send emails using gmail https://stackoverflow.com/a/47452/3107043