Hi James — thanks for the clear screenshots and description. Short version: this is almost always caused by Outlook trying to connect using basic (IMAP/SMTP) credentials while Microsoft now requires Modern Authentication (OAuth) for Outlook.com/Exchange accounts. That makes IMAP/POP/SMTP sign‑ins either fail or repeatedly prompt for a password in newer Outlook builds unless you use the Exchange/Outlook.com auto-configured connection or an app password. Here’s what to try, in order.
Why this is happening (brief)
- Microsoft has been deprecating Basic Authentication for Exchange/Outlook.com and moving services to Modern Authentication (OAuth). Clients that use IMAP/POP with Basic auth will see repeated prompts or fail.
- Outlook desktop will use Modern Authentication for Outlook.com only when the account is added as an Outlook.com / Exchange profile (automatic configuration). If you configure the same account as IMAP/SMTP in Outlook desktop, Modern Auth is not used and will likely be blocked.
- If you must use IMAP and your Microsoft account has two‑step verification turned on, you must use an app password for IMAP clients that don't support OAuth. Otherwise IMAP/POP may be blocked.
Step-by-step fixes (do these in order)
1) Update Outlook / check build
- Open Outlook → File → Office Account → About Outlook and note the version/build. Outlook 2021 needs a sufficiently recent build for full Outlook.com support. If Office isn't up to date, click Update Options → Update Now. Updating first avoids many compatibility issues.
2) Remove the IMAP account and create a new Outlook profile (recommended)
- Close Outlook.
- Open Control Panel → Mail (Microsoft Outlook) → Show Profiles → Add. Give the new profile a name.
- Use Add Account and enter only your full outlook.com address, then let the automatic setup run. When the Microsoft sign-in window appears, complete the OAuth sign-in (this is the Exchange/Outlook.com method that uses Modern Authentication rather than IMAP). This should create an Exchange/Outlook.com type connection instead of IMAP/SMTP.
- Set the new profile as the default and start Outlook.
3) Clear stored Windows credentials (common quick fix)
- Open Windows Settings → Search “Credential Manager” → Windows Credentials.
- Remove any entries that reference outlook, microsoftoffice, mso, or your outlook.com address.
- Reboot and open Outlook; when prompted, sign in via the Microsoft/OAuth dialog (not an IMAP password box).
4) If you intentionally want to use IMAP (manual) instead of Exchange autoconfig
- Be aware: Outlook desktop does not use OAuth for IMAP/POP, so Basic auth may be blocked by Microsoft. If your account has two-step verification you’ll need to create an app password in your Microsoft Account security settings and use that in Outlook instead of your normal password. If your tenant/organization has blocked app passwords, IMAP might not be allowed at all.
5) Run the Outlook troubleshooting tool / Get Help
- Microsoft’s diagnostics for Outlook sign-in problems are now in the Windows Get Help troubleshooters (classic SaRA diagnostics are migrated). Run the Outlook troubleshooters to collect logs and automated checks.
6) Other checks
- Temporarily disable third‑party firewall/AV to rule out interference.
- If you use a VPN or proxy, try without it.
- If Autodiscover fails repeatedly, some networks or DNS/firewall rules can block it — try from a different network (phone hotspot) to check.
What I need from you if this still fails
- Tell me the exact Outlook version/build from File → Office Account → About Outlook.
- Confirm whether the account has two-step verification / Authenticator enabled.
- Tell me whether you tried creating a new profile and what error (if any) you now see, or paste the exact message from the credential prompt.
Useful Microsoft docs (quick links referenced above)
- Modern auth and Outlook.com guidance.
- Deprecation of Basic Authentication in Exchange Online.
- Outlook and other apps unable to connect when using Basic auth (recurring prompts) — troubleshooting steps.
- POP/IMAP/SMTP and Modern Auth details (why IMAP may fail).
- How to create and use app passwords for Microsoft accounts.
If you want, I can walk you step‑by‑step through: (A) checking your Outlook build, (B) creating a new profile and adding the account so it uses Modern Auth, and (C) clearing Credential Manager. Which would you like to try first?