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[Binarus]

> If you want to see flame wars even more pointless and/or entertaining than this one, check out the mailing lists for DMARC. ;-)  They make these recent exchanges seem quaint by comparison.

I am sorry that this thread is not useful to you. I don't consider it a flame war. Every party (except the one who called us "phenomenally stupid") had a reasoning which at least is worth thinking about.
 
> FWIW, mailing lists and DMARC make a particularly noxious couple, as almost all mailing lists will break DMARC, and thus lead to all sorts of rejections.  That very subject is the topic of the most vitriolic flame wars on the DMARC lists. 

Maybe. We are currently not interested in DMARC.
  
> At the risk of perpetuating this severely off-topic thread, IMHO if "Binarus" is able to eliminate "90% solely by checking for SPF and DKIM" then one must question just what the rest of their anti-Spam measures were doing?

The answer is quite easy: Until now, there just haven't been any measures against SPAM on the server side. Instead, users have used Thunderbird's junk filter (which works great IMHO). So, before checking SPF / DKIM, the clients actually have received every message which hit the server, except the messages which were addressed to non-existent recipients. We know quite well how many SPAM got to the clients before and after implementing the SPF / DKIM checks.

The problem with letting the clients doing the SPAM handling (explained by the example of my personal account): Once per year, I had to go through the JUNK folder to see if there were false positives in that folder. Some weeks ago, this ended in manually searching through about 12000 spam message and thereby finding about 10 important *ham* messages.

Given some court decisions here in Germany, it could eventually be dangerous to not handle a message in a timely manner or even to never know about that message if the sender can prove that your server has accepted the message. Therefore, there is no way around checking your SPAM folder if you let your MUA sort out the SPAM.

Some weeks ago, for a reason I still don't know, the SPAM volume hitting our clients suddenly doubled (or tripled, I don't have the exact figures). Therefore, we have decided to change our SPAM handling. Nobody is keen on scanning 100000 SPAM messages at the end of the year (my mailbox is not the worst one) ...

By the way, I am now finishing my working day, having got exactly 4 SPAM messages (two weeks ago: between 200 und 300 per day).

Regards,

Binarus