Error sending mail via SMTP

[Gio]

Hi,
I'm trying to configure iTop to use SMTP instead of PHPMail to send mail via Exchange on Office 365.
I set followig line on "config-itop.php" file:

'email_transport' => 'SMTP',
'email_transport_smtp.host' => 'smtp.office365.com',
'email_transport_smtp.port' => '465', //tried also 587
'email_transport_smtp.encryption' => 'SSL', // tried also STARTTLS
'email_transport_smtp.username' => 'help@xxxx.com',
'email_transport_smtp.password' => 'xxxyyyy',

I tried also using gmail address, but the error is always:
"Error: 'Connection could not be established with host localhost [Unable to find the socket transport "SSL" - did you forget to enable it when you configured PHP? #1]'"

It seems like php does not find php-openssl, however phpinfo() shows:
openssl
OpenSSL support enabled
OpenSSL Library Version OpenSSL 1.0.2k-fips 26 Jan 2017
OpenSSL Header Version OpenSSL 1.0.2k-fips 26 Jan 2017
Openssl default config /etc/pki/tls/openssl.cnf

I'm using:
iTop version 2.3.3-3159 built on 2016-12-22 17:35:48
Data model: 2.3.0
MySQL: 5.7.28
PHP: 5.6.40

Any idea how can I get SSL SMTP working?

[Jeffrey Bostoen]

May we assume email_transport_smtp.host points to the proper O365 URL?
( since your error does seem to suggest it's trying to connect to localhost instead )

[Gio]

Yes, I forgo t to mention, string is:
'email_transport_smtp.host' => 'smtp.office365.com',