Firewall – Incoming emails not appearing or very delayed – Exchange 2003 w/ Barracuda Firewall

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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).

Best Answer

  1. Perform a DNS lookup for the MX record for your email domain.

  2. If step 1 succeeds then perform a DNS lookup for the A record returned from the MX record lookup.

  3. If step 2 succeeds then try to establish a telnet session to port 25 of the ip address returned from the A record lookup.

  4. If step 3 succeeds then try to send an email to an internal user from the telnet session established in step 3.

  5. If step 4 succeeds then you know the problem is between the Barracuda and the Exchange server.

  6. If the Barracuda has any type of CLI then try to establish a telnet session from it to port 25 of your Exchange server.

  7. If step 6 succeeds then try to send an email to an internal user from the telnet session established in step 6.

  8. If step 7 succeeds then you know the problem is with the Exchange server.

Let us know which step, if any, fails so can help you narrow down the problem.

I think I've covered all the bases. If anyone sees anything I've left out, please pipe up.

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