I cannot send email and I'm connected to the internet via iPrimus. Why?

To help prevent spam from the iPrimus network they made a change to their network which blocks you from sending mail on port 25. To correct this problem please see their announcement which we have copied and pasted below...

Primus Residential Broadband and Dial Up Customers.
Please be advised that iPrimus has recently begun blocking access to outside SMTP mail servers (Port 25) to try and reduce the amount of Spam coming from Virus infected, and compromised Zombie computers. This will mean you will only be able to send email using the iPrimus mail servers.

If you are using another internet service providers mail server, or running your own mail server, please ensure that you update your settings to send mail only through smtp.iprimus.com.au. Guides to configuring most email clients can be found on http://www.support.iprimus.com.au.

We apologise for any inconvenience caused.

Other isp's such as Telstra also practice this 'blocking'. iinet and Optus also block port 25 however it can be unblocked by logging into the isp's toolbox and changing a 'port blocking' setting.