Hi,

My system is running "Sendmail + Clamav-milter + Spamassassin" for implementing e-mail service.
In addition to Spamassassin, the Sendmail is also configured with DNSBL filtering with a few well-known lists (e.g. Spamhaus).
The combination is known to have rejected most of the obvious spams. However, complaints from users are still heard occassionally.
Some users tell me that proprietary products (e.g. IronPort) are much more effective.
I'm curious about the working mechanisms behind those commercial products, but can't find any detail.

My question is : Is it possible to achieve higher effectiveness in email spam filtering using only free software on Linux ?

Yes.

So let me guess, your next question is "how?"

Ensure your spamassassin filters/recipies are regularly updated. (Daily?)
Fine tune your rules/scoring, reducing the "spam threshold" may decrease the amount of spam "getting through" but may have an impact on legitimate mail.
Have a mechanism where your users can report spam and indeed report non-spam to allow you to fine-tune your filters or add new filters.
Make use of SPF records for any domains sending mail inbound to you and respect the SPF options if they are "strict", consider also how to deal with "loose" SPF records for domains.

Having done the above for a while I outsourced all inbound e-mail handling for my personal stuff and for work it's a combination of outsourced mail handling and outsourced filtering for anywhere we still have "in house" mailboxes.

1 members found this post helpful.

Thank you for the suggestions.

I'll try to implement them as many as possible.