Our main IT guy is out of the office, so I have to (quickly) resolve this urgent issue. No one in the company is receiving external emails. It seems to have just happened suddenly. We have an AD domain, using Exchange Server 2003, with a Barracuda 300 Spam & Firewall box as our inbound firewall. When I look at the Barracuda admin page, it shows messages having come in and processed for hours and then all of a sudden no messages, starting a few hours ago. In Exchange System Manager, there are a ton (hundreds or more) of SMTP connections between Exchange and the Barracuda box. Barracuda support is currently looking at the problem but finding nothing so far. Any ideas as to what this might be? Something from the Exchange side? Thanks in advance for any help.

EDIT: If I do a traceroute from an external address, it never reaches my firewall. I see the packets go from router to router on the internet, but the last router listed is Comcast, my ISP. It doesn't show our hardware firewall at all, so I'm thinking maybe the mail is never making it to the Barracuda box (and thus, on to the mail server).