What solution should be recommended for secure internal communication across departments in an organization using Microsoft 365?

The ideal solution for secure internal communication across departments in an organization using Microsoft 365 is Microsoft Teams. This platform is designed specifically for collaboration and communication within organizations, offering real-time chat, video meetings, and file sharing in a secure environment.

Microsoft Teams facilitates seamless communication and collaboration among team members and across departments. It provides functionalities such as threaded conversations, channels for various projects or departments, and integration with other Microsoft 365 applications. The emphasis on security within Teams includes encryption of data both in transit and at rest, as well as compliance with various regulatory standards, making it especially suitable for internal communications where data privacy and security are paramount.

While Outlook is a robust email service that supports communication, its primary function is email rather than real-time collaboration. SharePoint serves as a platform for document management and collaboration but does not focus on real-time communication. Microsoft Viva Engage is a tool for employee experience and engagement that can facilitate discussions and knowledge sharing, but it does not provide the comprehensive communication tools that Teams does.

Thus, for secure internal communication across departments, Microsoft Teams is the most fitting choice due to its purpose-built features for collaboration and communication.