Using MailValve EX with Office 365 in Hybrid Deployment

MailValve EX is implemented as a Transport Agent, and must be installed on an On-Prem Exchange Server. However, MailValve EX can be used to purify emails sent via Office 365 if Office 365 is used in Hybrid Deployment. (Office 365 + On-Prem Exchange Server)

You need to enable "Centralized Mail Transport" in the Microsoft Office 365 Hybrid Configuration Wizard, so that all outbound emails from Office 365 will pass through your On-Prem Exchange Server, and therefore will be processed by the MailValve EX Transport Agent before reaching their addressees. (see Transport options in Exchange hybrid deployments )