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. It's also possible that you were blocked simply for sending legitimate email that has a PDF file attached, or that breaks one of the many rules that each Barracude user can set on their own.
Here's a further explanation of why your IP address may have been listed:
Here's a page where you can request to be removed from their block list:
If you're so inclined, there's also a page where you can request to be registered with their system, which may help mail get through, but this is a paid service: https://www.emailreg.org/index.cgi?p=register
If you have any questions or need any assistance, please contact us by email or phone.