This is a hassle; I got two separate notifications from fellow MVPs that my Barracuda box was blocking their inbound mail. When I checked the Barracuda logs, sure enough, it had rejected both messages; the reason listed was “Intent (xmlsoap.org)”.
“Intent” is the status code the ‘cuda uses to indicate that it blocked a message because it contains a spammish URL; it’s essentially the equivalent of SURBL. I checked the two messages, and sure enough they contain a reference to xmlsoap: “http://schemas.xmlsoap.org/soap/envelope/”. However, this reference comes from the original message in the thread, which was an HTML message! Apparently somewhere in the round-trip reply cycle, the HTML version was converted to plain text, which exposed the xmlsoap reference, which the Barracuda improperly blocked. Evidently spammers have sent HTML-formattted mail from Outlook before, so xmlsoap.org has ended up on the intent list. Thankfully the Barracuda interface has an easy-to-find “Exempt this URL” link, so I could clear the ban, but it’s still not what I would’ve expected.