RBL lookup error

Not sure what you mean by DNS error at the source host.
Spamhaus keeps a list of blocked IPs. It will not do any further DNS lookups. If it times out, it either means spamhaus.org is having problems (haven't seen any), or your connection to them.
Also, some ISPs believe that RBL lookups put too much burden on their network and block access to spamhaus. You could try and use a different RBL to see if it helps.

An RBL won't do a reverse lookup to determine a host name. So yes, we agree it is an issue between your server and spamhaus.

Good question about the limits of free access. I wouldn't know if they throttle automatically or not.

The RBL keeps a list of all blacklisted IPs.

The receiving server (your server) will send a query containing the IP of the sending server to the RBL to see if it is listed.

Being the SMTP protocol quite old and due to the fact RBL lookups were not contemplated when it was created a hack/workaround is used in the form of a DNS query. Based on the return value of this query your mail server will accept or reject the message.

An example:
-Your server receives a connection attempt by a sending server at 194.123.321.001
-The lookup mechanism (handled by postfix or amavisd or spamassassin, but in your case postfix) will reverse the bytes and add the RBLs hostname. This results in: 001.321.123.194.zen.spamhaus.org
-Next a DNS lookup for 001.321.123.194.zen.spamhaus.org will take place.
-If it returns an address (usually in the 127.0.0.0/8 loopback block), it means the IP is listed. If it returns NXDOMAIN it is not listed and mail is accepted.

HTH,
Alex

Celia,

out of curiosity. Did you ever figure out what the problem was?

Alex

I might be having a similar issue here...

from /var/log/mail.log:

Sep 15 11:08:38 mail-CLEANED-com postfix/smtpd[2683]: warning: 240.132.85.209.zen.spamhaus.org: RBL lookup error: Host or domain name not found. Name service error for name=240.132.85.209.zen.spamhaus.org type=A: Host not found, try again

so I tried doing some host lookups from the cli:

mail-CLEANED-com:~ admin$ host www.google.com
www.google.com is an alias for www.l.google.com.
www.l.google.com has address 64.233.167.104
www.l.google.com has address 64.233.167.99
www.l.google.com has address 64.233.167.147
mail-CLEANED-com:~ admin$ host www.spamhaus.org
www.spamhaus.org has address 64.124.52.228
www.spamhaus.org mail is handled by 10 smtp-ext-layer.spamhaus.org.
mail-CLEANED-com:~ admin$ host zen.spamhaus.org
Host zen.spamhaus.org not found: 3(NXDOMAIN)

Hrmmm....
Any thoughts Alex?

Host zen.spamhaus.org not found: 3(NXDOMAIN)

This is normal. zen.spamhaus.org will not return any response. Only the host lookup records like:
194.249.233.219.zen.spamhaus.org
will/should. If they don't you need to investigate why spamhaus queries do not go through (ask ISP).

Just wanted to let y'all know that I talked to the sysadmin at my ISP, and he had this to say.

"SpamHaus doesn't like our DNS servers, but I have a work around. It should work for you now, but lemmie know if you still have problems."

I don't know what he did, but it works now. 🙂 So, I recommend talking to your ISP or DNS administrator.

Thanks for your feedback.

Spamhaus would probably only block you if you go way over the fair use (free use) limits.

I have however seen quite a few ISPs blocking access to spamhaus.

Glad you got it sorted and that your ISP was willing to fix things for you. 🙂