I have been asked about the blacklisting and the spam filter recently.
Actually I am working on the topic of spam filters momentary at background.
I am pretty interested and trying to figure out which spam filters are used by whom for most important local ISPs.
SpamAssassin is a spam filter, widely used by middle and small ISPs, who haven’t developed their own filters, like the biggest local provider “webmail.co.za” in South Africa.
So, in my opinion, it’s not less important.
This filter stamps every mail with a score, normally a score less than 50 is qualified as non-spam.
The ISP can change a bit on the matrices to get a better control of the strictness for anti-spamming.
Barracuda is a blacklist as well as a filter.
As a blacklist, Barracuda is not as huge or important as Spamhaus, but we should not over see it.
In some countries, like India, Italy, the local providers look up this list to filter incoming emails.
So it is a so called filter deciding to receive or bounce.
As a spam filter (spam filter decides into inbox or spam folder. With the precondition, the mail is received by ISP), I haven’t seen often. So I suppose, it’s not so important.