We primarily use the solution for disaster recovery. We are on Office 365 as well, and it is a bit redundant. 

We are using Mimecast Mailbox Continuity for the security of email from threats, such as spam, fishing, and viruses.

We are currently doing a POC with the solution.

Our primary use case for the solution is for monitoring emails. It also flags and highlights suspicious and new emails. Overall, it protects from malicious emails within or outside of organizations. Mimecast Mailbox Community is an email gateway required for every organization, regardless of size.

We primarily use this product to journal our email. If there is a disaster, for example, and our primary and secondary data center goes down, we can turn it on for email continuity. 

We don't take advantage of the archiving capability.

We use it for email availability. In case our on-premises mail servers go down, we switch over to this solution. 

We also use it for security. It has a security element, and it does malware checks. We are looking into purchasing Mimecast Email Security 3.0.