Suddenly external email to our company stopped reaching our building, while internal email continues to function.
We have a Sonicwall which directs the email to a Barracuda Spam filter, which sends it to our Exchange 2010 Server. There is no mail reaching the Barracuda. The NAT policy in the Sonicwall to send the mail to the Barracuda appears to be intact and nothing there has been changed. I have restarted both the Sonicwall and the Barracuda.
I went to mxtoolbox.com and did an MX lookup for one of our domains. It looks correct. Then I did a DNS lookup which looks okay too. When I did an SMTP test, it says "No connection could be made because the target machine actively refused it (my public ip address):25"
I am not sure what to do at this point, any help is appreciated - thank you.