You want to know how to generate a Certificate Signing Request (CSR) without specifying Organizational Unit data due to deprecation of the OU as part of public certificates.
Release : 10.7.5
Patch 292 for version Messaging Gateway 10.7.5 removed the requirement for an Organizational Unit when creating a certificate request. This will also be included in future versions of the product.
Information on patching the Messaging Gateway can be found here:
For older versions, as a workaround you can create a Certificate Signing Request elsewhere and then have the certificate signed and import the certificate and key into the Messaging Gateway with the help of these articles: