Closing this to consolidate. For anyone landing here: ErrorNamespace / User is authenticated but not connected right after a successful sign-in means IMAP is disabled for the mailbox (either by your organization, or in Outlook.com → Settings → Sync email → “Let devices and apps use IMAP”, as the last reply found). We’re planning to add Microsoft Graph API support so that Office 365 / Outlook accounts no longer depend on IMAP being enabled; updates will be posted in Institutional Office365 not working.