SMTP Error: Could not connect to SMTP host.

I'm running Wordpress and the mail doesn't work.  I installed Configure SMTP plugin to wordpress and I had error.

SMTP Error: Could not connect to SMTP host.

SMTP Host:  Localhost
Port: 25.   

I tried Port 587 and 2525, it didn't work.
I checked the postfix and dovecot and they are running.  I also send email via server and it work.   
I disabled Firewall and it still didn't work.

NOTE: I solved this temporarily by using external SMTP such as smtp.google.com, my own smtp server and https://sendgrid.com/

any help is greatly appreciate.

Wordpress SMTP will work on PHP 5.4 (default) or PHP 5.5.   If you switched it to PHP 5.6 or PHP 7.x, Wordpress' SMTP or phpmail may not work.   You have to have your own external mail server SMTP to make it work such as Google SMTP or CyFocus email http://shop.cyfocus.net/email/email-hosting.aspx?ci=12940&prog_id=cyfocus