.Net Jonesie - Spam & ISP's

Thursday, May 11, 2006

I've been getting a lot of spam at work lately that is getting through our normally very efficient filter. It gets through because the senders address 'looks' valid, isn't black listed and the content of the email is a single jpg. For the spammer this is not so great because they can't put hyper links in the message so even if I was inclined to read the drivel they promote then I'd have to manually navigate to some stupid web site. I'd be very annoyed if I was paying for these emails to go out.

However, the real issues is how to block these. The simple answer is to use gray-listing - not sure if this is the correct name but this is what my wife does - I think it goes something like this:

Email is received. Receiving server check's it's white-list of senders and finds that the email address is unknown.
Receiving server pings the senders domain email server and asks it to verify the address.
If the senders server doesn't respond at all then it's most likely spam and email is gray-listed
If the senders server responds with an OK response then the email is let through - at least to the next level of checkinig.
If the senders server responds with an error or BAD then the email if gray-listed or blocked.

Users are able to view gray-listed messages and unblock senders or whole domains.

This sounds very simple and logical but it's very suprising how few ISP's do this. Despite the advertising campaign Telecom don't do spam checking of any consequence. My wife used to use Xtra but when she found out that they will allow through emails from non-existant Xtra accounts that didn't come from one of there own servers, well this was the last straw I think.

For my personal email I have my own server on my hosted domain. It uses spam assassin which does a reasonable job - I get about 5 on a bad day. What's your ISP like?

Thursday, May 11, 2006 9:23:25 AM (New Zealand Standard Time, UTC+12:00)

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