How risky is connecting Claude to our whole Microsoft 365 setup?

First ask what he actually wants it to do. Summarizing a calendar is a different request from reading every accessible document or sending mail.

Then review the connector's requested permissions and consent scope before enabling it. Start with the smallest set needed for a specific task, and check whether the permissions are limited to the signed-in user or grant broader organizational access. Review existing SharePoint and OneDrive sharing too, since an assistant may surface material the user can already access but didn't realize was shared.

For email, I'd start with drafts and require a person to review and send them. Confirm what the connector can actually do rather than assuming it can or cannot send.

Make the subscription an organization-managed account rather than a personal one, if the chosen plan supports that. Get the security or compliance person involved, and put the proposed access, risks and approval in writing. Leadership can accept a business risk, but they should know what they're accepting.

Check the applicable contract and plan terms for data retention, model training, processing location and access to stored data. Don't assume every paid plan has the same terms. Depending on the business, customer agreements or government contract requirements may need a look too.

Worth comparing this with Microsoft 365 Copilot before building out a separate connector. The experience and available models may differ, and using the same model doesn't automatically mean the data path or controls are the same.

Check the actual product configuration, licensing, permissions and privacy terms for each option. A Microsoft-managed route may fit existing governance better, but it still needs a permissions review.

Give him a short training session before turning it on. Show him that a polished draft can still contain wrong figures or disclose information to the wrong recipient. Make final review a clear expectation, especially for external mail.

If the approved setup is too hard to use, people may look for personal accounts instead. Make sure the company has a clear way to request access and knows how it will handle unapproved connections.