OroMailCenter is using the Firebird database engine. Firebird is a robust database and is "Open Source" and available for free. You don't have to buy separate licenses for a solid database engine.

Firebird is also multi-platform, which means that the OroMailCenter database can be located on a computer with any of the following operating systems: Windows®, Linux® or Solaris® and more. So, OroMailCenter is perfect for large enterprises with hundreds of users as well as for a stand-alone use.