Cause:
This Barracuda issue happened because an IP address that you are taking from your ISP (Internet Service Provider) is blocked.
Symptoms:
If you are using outlook, it may gives the following error:
Task '<Account Name> - Sending' reported error (0x800CCC0F) : 'The connection to the server was interrupted. If this problem continues, contact your server administrator or Internet service provider (ISP). The server responded: 550 http://www.barracudanetworks.com/reputation/?pr=1&ip=<your IP address number>"'
Solution:
If it is static 'fixed' IP address (by means that you always have this IP address "for example 41.130.44.200" as a request from you to ISP), so either them or you have to request removal of this IP from barracuda.
http://www.barracudacentral.org/rbl/removal-request
If it is dynamic IP address (which means that if you switch off the router and switch it on again, you’ll get different IP address), so when this error happens again, switch off and on the router and try sending again. (Your ISP should be reported anyways for their blocked IP addresses).
In order to know if you have static or dynamic IP address, use the following website:
http://whatismyipaddress.com/
switch off and on router for 10 sec. and access the above link to see if your IP has changed or not.