Mimecast for Outlook (or MfO) is an application for Windows that provides Outlook users access to Mimecast features.
It used to be known as MSO (Mimecast Services for Outlook) and the application itself was called the MSO Plugin.
The tool and configuration tool can be downloaded from here.
Users of Exchange or Office365 can take advantage of the additional benefits that MfO provide.
There are several versions of Outlook (Office) and several versions of MfO, so you need to ensure you check which version is appropriate. In this example, the screenshots are from Outlook 2007 32 bit, and Mimecast for Outlook 6.1.1434.14830 (32 bit).
After installation and launching Outlook, new Mimecast options will be available:
If no exchange account is configured, a notification like this will appear:
Otherwise, you can move to the next step of configuring and using MfO.