What’s going on with Barracuda blacklist results?

You may be seeing something odd with listings on Barracuda right now.  MxToolbox is reporting your IP address as listed on Barracuda’s Blacklist but when you go to Barracuda’s website, you’re not listed.  You’re probably thinking “These guys at MxToolbox have lost it”, but that’s not quite the case.  

MxToolbox subscribes in various ways to the DNSRBLs at different providers like Barracuda.  Barracuda being a large organization with a large subscriber base has multiple DNS servers providing blacklist information.  One of these servers seems to be out of sync with the others and the website database.  The questionable IP addresses appear to be coming from this one server.

Why does MxToolbox report it as blacklisted?

The MxToolbox philosophy on blacklisting is to provide blacklist results that most closely resemble real-world blacklist usage.  To do that, MxToolbox caches positive blacklist results until the TTL (time-to-live) of the record expires.  When we get a positive response, we list it regardless of how many of the DNS servers list it at the blacklisting organization, because this is how spam filters work. A spam filter will get a positive result and lock out any email from that IP address.

Am I really blacklisted even if I’m not on Barracuda’s website?

If you are listed on the out-of-sync DNS server, you are technically blacklisted.  Spam filters that subscribe to Barracuda may connect to this DNS server,  receive your IP address on the blacklist and then begin to refuse your email.

What can I do?

To get off the blacklist, you must contact Barracuda and let them know that you are listed on one of their servers.  When we investigated, we found the results were coming from a server in their geons01.barracudacentral.org DNS server pool (see the image below).  We have opened our own case with Barracuda.

Three direct lookups of a particular IP address on Barracuda's DNS servers.  Note that the same server pool provides different results.

Three direct lookups of a particular IP address on Barracuda’s DNS servers. Note that the same server pool, geons01, provides different results.