2015-12-15 16:58:49 SMTP -> get_lines(): $data is ""
2015-12-15 16:58:49 SMTP Error: Could not connect to SMTP host.
2015-12-15 16:58:52 SMTP -> get_lines(): $data is ""
2015-12-15 16:58:52 SMTP -> get_lines(): $str is ""
You’re probably running into the fact that PHP 5.6 now verifies SSL certificates by default, and if you connect to a server that doesn’t verify, the connection will fail. Diagnose your situation using openssl. if this is what’s happening, you can provide additional params to the SMTP connection to tell it not to verify certificates, though of course that means your connection is no longer secure.
It’s the same as an SSL cert for a web server – it needs to match the domain, be signed by a trusted CA (i.e. not self-signed), and should have an SHA2 hash and use a 2048-bit key. How you install it depends on your specific server – and it will tell you in its docs.