Your ability to use your own domain name as the outgoing SMTP server is limited by your ISPs mail policy.
In most cases, ISPs will block any attempt to send email via a 3rd party server such as this. This is also known as "blocking port 25 outgoing"
To resolve this issue, change your SMTP/outgoing server name to the one supplied to you by your ISP.
Doing this doesn't make the "from" information of your emails look any different.
Some common ones are:
iiNet: mail.iinet.net.au - or - mail.m.iinet.net.au
Please contact your ISP directly for any specific information regarding the above outgoing settings.