Alexandre Chapellon wrote:
When other well known DNSBL (I have always heard spamhaus sbl and xbl are trust worthy) list less at most 50 entries , barrcuda lists almost 8000!!!!
That's not a problem all by itself, but when combined with this:
Finally there is a special feature that barrcuda folks call "deep scanning" which makes the appliance scans the 'Received' headers and reject the mails if an IP found in that headers, is listed in the DNSBL... a feature that should obviously be called: 'even increase my false positive rate'
... it makes life difficult. (In fact, if you provide Internet access for residential customers, a big chunk of your IP address space *should* be listed on Spamhaus' PBL - these IPs should be using your SMTP relay, or submitting mail via SMTP AUTH to another relay, not contacting recipient MXes directly.)
I've had far too many incidents in the last ~6 months of having tech support ask me to dig into why a certain customer of ours is suddenly getting postmaster rejections on their mail to certain recipients - usually "important business contacts".
All of them have proven to be recipients behind a Barracuda filter appliance that's deep-scanning headers and rejecting the message based on our customer's connection IP on our network - an IP behind our standard block for SMTP to anywhere but our own SMTP relay... and the rejected message was properly relayed through that system. Or worse, an IP on some other provider's network, where our mail customer is using SMTP AUTH on port 587 to relay through our server.
I usually tell tech support to tell the customer that they'll have to contact the recipient by eg phone to let them know they're missing legitimate mail.
-kgd
