[CentOS] spam control

[Bill Church]

Quoting DamianS <clovis at iinet.net.au>:

> There is a way to block 99% of spam though.
> That solution is for ISPs to start charging money for each email sent!
 
Really? So you mean the spammers that own 10,000+ node botnets, comprised of grandparents and neglected school PC's will stop sending out SPAM because of the owners of the PC their using will get a bill? They don't care, they already take over someone else's PC to do their dirty work, they have no conscious.
 
To really stop it cold mail needs to be brought up to 2006 technology. So far everything to fix SPAM has been a band-aid. The current e-mail technology and system was created when the Internet was based on trust, this is obviously no longer the case and a suitable replacement needs to be created.
 
The other issue is lax administrators (e-mail, desktop, system, etc...). If people would stay on top of security holes, or provide adequate protection to their customers / users the spammers would have a hard time taking over their PCs to do their dirty work.
 
For now, the best bet is a well maintained reputation system or black list, grey listing on top of that, enforcing strict DNS ptr and a records (this will cause false positives, but if enough people take a stand lazy administrators will have to eventually fix their crap DNS), utilizing SPF and Sender Keys, and a good reactive filter. Also, another good method is limiting clients sending to invalid recipients, say if more than 3 invalid recipients are sent block further attempts from that client. I've not done this in SA or anything else, but an appliance I use allows me to do this, and it's quite effective.
 
AOL, as much as people hate them, has the best chace of fixing a lot of these problems as they enforce a lot of these things already (http://postmaster.aol.com/).
 
If you have the luxury of blocking IPs based on countries or regions, that helps as well but not everyone can do this.
 
-Bill