Using htmlMimeMail5 for sending emails

[StrangerInBeijing]

I am trying to get to send email from my development machine, which is pretty much the same setup than the new server (Windows, Apache, PHP5, MySQL...using WampServer).

My own email (which I use for development), and the company email (for which I still need the smtp details..i'm new here), are hosted by seperate companies abroad in UK.

I want to perform various actions such as sending html emails, etc, and as I am not a PHP expert, I did some research, and using htmlMimeMail5 looks like a good package to use for this.

However I am having problems to get this work.
Let's say my own email details are as follows:
SMTP server: authsmtp.streamline.net
SMTP username: [email protected]
SMTP password: 1234
SMTP port: 25

Apparently first thing I had to do was to change these lines in my php.ini, which I did (and yes, restarted all services):

[mail function]
; For Win32 only.
SMTP = authsmtp.streamline.net;

; For Win32 only.
sendmail_from = [email protected];

For htmlMimeMail5, I could not find documentation about what to change, but I changed the following:

        * Defaults for smtp sending
        */
        if (!empty($_SERVER['HTTP_HOST'])) {
            $helo = $_SERVER['HTTP_HOST'];

        } elseif (!empty($_SERVER['SERVER_NAME'])) {
            $helo = $_SERVER['SERVER_NAME'];
        
        } else {
            $helo = 'authsmtp.streamline.net';
        }

        $this->smtp_params['host'] = 'authsmtp.streamline.net';
        $this->smtp_params['port'] = 25;
        $this->smtp_params['helo'] = $helo;
        $this->smtp_params['auth'] = false;
        $this->smtp_params['user'] = '[email protected]';
        $this->smtp_params['pass'] = '1234';

However, I still get this error:

Warning: mail() [function.mail]: SMTP server response: 551 User not local; please try <forward-path> in C:\wamp\www\lab\email\htmlMimeMail5.php

While I am at it. Am I missing something, or why is it such a hassle to send a html email via an external smtp server? Does not really make sense to me.