This issue has been addressed in patch 291 for Messaging Gateway version 10.7.5. To resolve this issue, upgrade to 10.7.5 if you are not already using it, and then apply patch 291 or greater cumulative patch.
For information on patching the Messaging Gateway appliance, please see the following article:
Installing and removing patches for Messaging Gateway
As of the publishing of this article, Messaging Gateway version 10.7.5 is the current fully supported release, previous versions have not been evaluated. It is highly recommended to keep the Messaging Gateway fully updated to have access to the latest security updates.