Where would you start with Outlook disconnecting every few minutes?

First, work out whether this is Outlook or the account/service. Have an affected user keep Outlook on the web open while the desktop app disconnects, and check Microsoft 365 service health. If web access is steady, focus on the desktop client and its network path.

Check Outlook's connection details while the problem is happening. Hold Ctrl and right-click the Outlook tray icon, then open Connection Status. Repeated authentication reconnects point you in a different direction than connections that drop alongside network changes.

Look at Entra sign-in logs for the affected users and match the timestamps to the disconnects. Check for failed or interrupted sign-ins, Conditional Access results, and MFA or token-related prompts. The three-day sign-in frequency alone doesn't establish the cause, so verify what the logs show.

I'd also compare networks and check whether other apps lose connectivity at the same time. VPNs, proxies, or TLS inspection can complicate the connection, especially if several users share the same network path. A connectivity test can help narrow down Exchange Online access issues.