Gary Davis' Blog

DotNET/PayPal Development and other Techie Stuff
posts - 47, comments - 170, trackbacks - 0

How I Blocked Spam Coming Into my Home Email Server

Some time ago, I blogged about setting up my home email server to support incoming email using the service (How I Solved Comcast's Block of my SMTP (Email) Port 25). Most of my incoming email is through the site but in this case, it is business-related email for my wife’s site, which is hosted by the same home server.

The Webguild email was spam-filtered fairly effectively but the email coming in to Debsrealty via Rollernet was leaking lots of Canadian pharmacy and other spam. Lots of this spam is originating from some network of infected computers like the Waledac botnet). These spam emails are very difficult to block using the Outlook rules so I logged on to the Rollernet account to see what they offered for spam filtering support. It turns out there is pretty good support.

There five filtering options available.  RollernetFilteringI had not configured any of them but two of the five were already enabled (DNSBL and SPF). I then turned on two of the remaining three options (Greylisting and Anti-Virus) to see if that solved the primary problems. Greylisting keeps track of incoming emails looking at three things (sender’s IP, From and To). If it is new, it replies to the sender to retry later. Normal senders will retry but spambots don’t bother. Retries are passed on by the filter and it remembers so future email with the same “triplet” are pass without delay. This technique is very effective and did successfully block all of the pharmacy spam that Deborah was receiving. There are logs of all incoming email kept by Rollernet to see whether or not an email was filtered and why.

The final option is the SpamAssassin filter which looks at the content to see if it can recognize spam and add **SPAM at the start of the Subject of suspicious emails (easily checked by Outlook rules). SpamAssassin assigns a score to each email on how certain (on not) it is that the email is spam. Then you specify the score that you want to use and if an email has a higher score than your threshold, it will be flagged as mentioned (or you can block it). I may enable this if Deborah gets more spam not blocked by the other methods.

Print | posted on Sunday, March 21, 2010 12:00 AM | Filed Under [ Personal ]


No comments posted yet.

Post Comment

Please add 7 and 2 and type the answer here:

Powered by:
Powered By Subtext Powered By ASP.NET