External Outbound Mail Servers (SMTP)

25th of September, 2007

Most people aren't particularly careful with their computers. As a result quite a number of residential PCs are infected with virii, worms and spam relay agents. In an effort to contain this malware, a number of ISPs have elected to prevent their customers from connecting to outbound mail services outside of the ISP's own network.

This probably isn't a big deal for most people, as the majority of ISP customers use the email account provided by their ISP, even though they probably shouldn't. This only starts to become an issue if you're using an outside service to send your email, like a corporate mail account for work, or your own externally-hosted domain name.

Given the technical nature of this, most people tend to assume that there's something wrong with their email service, when in fact it's just their ISP being a responsible netizen and getting in the way of business. I take a number of calls each week about this, so I figured I'd make a post and do my part to help people search for this information themselves.

If your ISP allows you to disable outbound port filtering for SMTP (Port 25) you can usually do so via the customer portal on their website. I've provided a couple of links here to help people find their way, but if your Australian ISP isn't listed here and they do have a control panel for this, please let me know and I'll add the link.

ISP	Policy and Method
BigPond Internet	BigPond block port 25 on residential ADSL. ADSL with a fixed IP address, or BigPond cable is not affected. Telstra do not allow you to unblock this port. Instead you must upgrade to a fixed IP service. I suggest calling and asking them why.
Optus Internet	Visit the Optus Member Services Mail Filtering page and login with your primary account username and password.
Internode	Visit the Internode E-Mail configuration page and login with your ADSL username and password.
iPrimus	iPrimus block port 25 on all but the top-end corporate services. They do not allow the port to be unblocked. You could call them and ask them why.

Lastly, if you have some influence over the configuration of the external SMTP service you wish to connect to, you may want to suggest that an additional service running on port 2500 (in addition to 25) be implemented to allow users on the more draconian ISPs to connect.