Spam issues and how to overcome them

[Nathanael D. Noblet]

On Sat, 2016-06-11 at 10:46 -0400, Homer Dokes wrote:
> Greetings all,
> 
> So after having employed two kolab servers for over a year now, spam
> is 
> still a huge problem.

So I never found the tools Kolab used to be effective from the get go.
Fighting spam is a semi-complicated thing to do. Setting up a mail
server is something that you need to be knowledgeable about to get
right, never mind adding in spam filtering. I'll tell you however two
bits that before I started using Kolab made the biggest difference in
our spam.

#1 - Use Real time blacklists. The most effective for us is
barracuda's. Its free but you have to provide them with the IP address
your server will make requests from. Once added the amount of spam
dropped for us about 70-90% depending on the day. 

#2 - It also helps to reject by default a handful of other non-standard 
type of mail

#3 - Use a greylister. A greylisting program will watch mail arriving.
If it doesn't recognize the IP/sender. It will tell postfix to send a
temporary error. It does this for some configurable amount of time. For
us its 10 minutes. This stops quite a bit of spam as well because they
don't try over and over.

So in my postfix main I have the following:
smtpd_recipient_restrictions = permit_sasl_authenticated,
        reject_invalid_hostname,
        reject_non_fqdn_sender,
        reject_non_fqdn_recipient,
        reject_unknown_recipient_domain,
        reject_unauth_pipelining,
        permit_mynetworks,
        reject_unauth_destination,
        check_client_access hash:/etc/postfix/rbl_override,
        reject_rbl_client b.barracudacentral.org,
        reject_rbl_client sbl.spamhaus.org,
        check_policy_service unix:/var/spool/postfix/postgrey/socket

#4 - We use dspam for spam filtering. Once trained with a sufficient
corpus of mail I have found it to be better than anything else. When I
found the program, it was still being developped but that has tailed
off quite a bit but it still works well for our purposes. Here you have
to know what you are doing when you set it up. It is similar to Amavis
but in my opinion works better.

Hope that helps,
-- 

Nathanael