Setting up a WordPress instance, I need to use PHP-SMTP for email sending. I knew SELinux was giving me grief!

getsebool httpd_can_sendmail
getsebool httpd_can_network_connect

Then to change the settings:

sudo setsebool -P httpd_can_sendmail 1
sudo setsebool -P httpd_can_network_connect 1

Mind your security.