I'm having a similar problem with the plugin. I'm using Wordpress 4.0 and it is not working as it previously was. I've tried both gmail and yahoo SMTP server information and both fail to send test emails. I've also tried sending to different email addresses on different servers. I also deactivated all other plugins and it still doesn't work.
The SMTP debugging output is:
SMTP -> ERROR: Failed to connect to server: Connection timed out (110)