Can only receive first test email, then no more sending

[joebordes]

Do you have the field "From" set? Try leaving it empty, this is 90% of the cases.
Also, note that PHP5.6 has changed the way they treat secure connections. On that version and forward you must have a valid domain certification for encryption to work. You can use the options of "not validated" if that is your case.

Any firewall on the server?