This article is for customers using Barracuda as an incoming gateway and are having issues receiving email from SMTP2GO.
1 - Remove the SMTP2GO IP address(es) from the "Trusted Forwarders" list - if it has been added.
2 - Add the SMTP2GO IP address(es) to the IP Exemption list. You can find this in the "Block/Accept" tab followed by the "IP Block/Exempt" option.
If you're not using dedicated IP address(es), you can find a list of addresses to add to the IP Exemption list in this support article.
Additional information that may help is provided in an article on Barracuda's website, which suggests that 'sender spoof protection' should not be enabled:
The Barracuda Email Security Gateway has the option to prevent spoofing of an organization’s own domain by blocking emails with that domain name in the "From" field that are sent from outside the organization. Note that sender spoof protection should not be enabled if the organization sends messages from outside their internal email infrastructure (e.g., in the case of marketing bulk-mail services).