Spam firewall in inbound only mode ends up on DNS blacklists, how?

Hi, the title pretty much says it all. We have a Barracuda Spam Firewall 400 in INBOUND mode only. It is not passing any outbound mail. However somehow, as of this morning, it has ended up on the CBL, Spamhaus, and Barracuda Networks blacklists. Can someone explain to me how this is even possible?

Thanks.
IvrnetAsked:
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Kieran_BurnsCommented:
They should tell you why you are on the list if you query your domain name against them. My immediate reaction was a lack of reverse DNS which is something they complain about
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IvrnetAuthor Commented:
Well, I already called Barracuda and they're looking into it for me.

However, what does reverse DNS have to do with an inbound spam firewall? Nothing is being sent out through it.
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Kieran_BurnsCommented:
If the MX record of your domain points to that device as your inbound mail server it is meant to respond to reverse DNS queries... if it doesn't then spamhaus and the like bitch about it. (as it may imply a 'dodgy' server)
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IvrnetAuthor Commented:
Hmm, I see. Okay, well we'll see what Barracuda says. Thanks.
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