TL;DR: Outlook error 0x800CCC0E: “Cannot connect to the server” on an IMAP account

The fix only. No explanation, no diagnosis. Read the full article if any of this does not match what you are seeing.

1. Confirm the account works in webmail. If it does not, the problem is the account or password, not Outlook.
2. Gmail or Yahoo, and the error began after a password change or in 2026: close Outlook, open Credential Manager > Windows Credentials, remove the entries that start with MicrosoftOffice16_Data:OAUTH2 and contain tp_google_imap_Oauth2 or tp_yahoo_imap_Oauth2, restart Outlook and sign in again.
3. Any provider: test that the PC can reach the server on the right port (PowerShell).

Test-NetConnection imap.example.com -Port 993
Test-NetConnection smtp.example.com -Port 587

TcpTestSucceeded : False means something between you and the server is blocking it (firewall, ISP, wrong host name). Try another network, such as a phone hotspot.

4. Check the account settings against your provider's published values. Normal IMAP is port 993 with SSL/TLS. SMTP is 587 with STARTTLS (some providers use 465 with SSL/TLS). Tick "My outgoing server requires authentication".
5. Antivirus with an email-scanning or "mail shield" feature: turn off only that feature for a test, then back on. Do not turn the antivirus off.
6. Still failing and Gmail or Yahoo: delete only the matching key under the Outlook Identities registry path.

Export the registry key first (right-click it, Export). Touch nothing else.

7. Verify: press F9 in Outlook. Sending and "Synchronizing subscribed folders" should finish with no error.

Do not switch to NTLM or "Secure Password Authentication" unless your provider tells you to. It does not fix this error.

← Full article, with the diagnosis and the why