1. Export wildcard pfx from Windows machine
2. Download openssl for windows – http://gnuwin32.sourceforge.net/packages/openssl.htm
3. Copy wildcard pfx to machine where openssl was installed
4. Run the following commands:
   openssl.exe pkcs12 -in nameofwildcard.pfx -nocerts -out Keyname.pem
   openssl.exe pkcs12 -in nameofwildcard.pfx -clcerts -nokeys -out Certname.pem
   openssl.exe rsa -in Keyname.pem-out Keyname-nokey.pem
5. Open up barracuda interface and go to Advanced – Secure Administration
6. In the Trusted (Signed by a trusted CA) section, add Certname.pem into the Signed Certificate field and keyname-nokey.pem into the Private Key field.
7. Click Upload.
8. Change Certificate type to “Trusted (Signed by a trusted CA)”
9. Save changes

Credit to Cycure for a well written openssl guide.