Administrators with hybrid Exchange Server environments are urged by Microsoft and the US Cybersecurity and Infrastructure Security Agency (CISA) to quickly plug a high-severity vulnerability or risk system compromise.

Hybrid Exchange deployments offer organizations the ability to extend the user features and admin controls of the on-prem version of Exchange within Microsoft 365. Hybrid deployment can serve as an intermediate step to moving completely to an Exchange Online organization, Microsoft said.

The benefits include secure mail routing between on-premises and Exchange Online organizations, mail routing with a shared domain namespace (for example, both on-premises and Exchange Online organizations use the @contoso.com SMTP domain) and calendar sharing between on-premises and Exchange Online organizations.