Knowledgebase: Miscellaneous
Removing an IP address from the Barracuda blacklist

If the Barracuda network has listed your IP address as "poor," you may be unable to send email to mail servers that use Barracuda as a SPAM filtering service.

Here's a further explanation of why your IP address may have been listed: 
http://www.barracudacentral.org/lookups/reason

Here's a page where you can request to be removed from their block list: 
http://www.barracudacentral.org/rbl/removal-request/99.100.110.206