I used the PHP mail function for the first time today. I had to configure the SMTP setting for my mail server in my php.ini file and after that it worked fine. Still only sending plain text email, and I’m not sure that I can for HTML email. :P
I had a problem where my postfix mail system wasn’t listening on its IP address 10.1.1.123 but it was listening on 127.0.0.1. I checked my firewall settings and made sure port 25 was open, but I still couldn’t connect.
I read an article, Bind Postfix Mail Server To Localhost or Specific IP Address Only, which gave me the hint I needed.
The trick was to comment out inet_interfaces in /etc/postfix/main.cf because it was specifying loopback-only which meant postfix wasn’t listening on its other IP addresses.