British ISPs have reacted strongly to the suggestion of Trend Micro CTO David Rand that the ISPs should actively combat the problem of spam on the internet.

Rand’s suggestion is the blocking of TCP port 25 (the port used for SMTP, or email, communications between servers on the internet), making contact with customers who they suspect may be the source of spam outbreaks, as well as stronger government legislation.

The legislation idea has merit, after all the lack of cooperation between government agencies is how many international spam operations manage to go unpunished.  The blocking of SMTP on the other hand is impractical and costly to implement, both from a technical and a service perspective.

The basis of the idea is this.  Customers send mail using SMTP, therefore by blocking SMTP and requiring that customers send mail via the ISP’s mail servers allows close monitoring of email traffic and detection of spam.

The solution is problematic though because many ISP customers, both home users as well as businesses, have perfectly good reasons to not send their email via their ISPs mail servers.  These customers would need to be unblocked from using SMTP, and hence cannot be closely monitored.

The monitoring itself also presents two problems – firstly customers object to having their email correspondence inspected by other parties including their ISP.  Secondly, any false positives could have disastrous consequences if important emails were blocked.  ISPs do not want the exposure to liability if they block an email that results in monetary loss for the sender or recipient.A serious issue is also that of costs.  A higher email load combined with more thorough monitoring means more costs to the ISP for servers and software to do those jobs.  The human resource costs also increase, both in the management of the systems as well as the teams who need to contact and support customers who are suspected of sending spam.

Although email is currently the largest source of spam on the internet there are other forms of spam that are quickly becoming very common that would not be addressed by this solution.  Social networks such as Facebook and Twitter have become rich hunting grounds for spammers and phishers who are able to target victims with highly personalized attacks thanks to the open nature of these networks.

In a world where ISPs block spam email from customers the focus of botnets would simply shift to exploiting social networks and identity theft for the same outcomes.  Because these networks run simply as interactive websites they become impossible to block at the protocol level, and blocking them on a site by site basis would immediately outrage customers.

The British ISP heads who commented are correct in their view that businesses and email administrators need to take the responsibility of blocking spam that is sent to them, rather than expect ISPs to do all the work for them.