Cannot connect to outlook server

Question

Cannot sign in Microsoft Outlook keep getting cannot connect to the sever. Only the outlook server

Answer 1

Hi there, Thanks for posting here in Microsoft Community. Just to be sure what device does the issue is happening? Also, are you using the Outlook app or are you accessing the Outlook on a web browser?

Answer 2

Follow these steps to troubleshoot Outlook not connecting to the server on Windows 11:

1. Check if the issue is only with Outlook
   • Confirm that other internet services (websites, other apps) work.
   • If only Outlook fails, continue with the steps below.
2. If using IMAP/POP (non-Exchange account), fix possible app password issues
   • Sign in to the email provider’s webmail in a browser.
   • Go to Account Information > Security and create a new App Password for Outlook.
   • In Outlook:
     1. Select File.
     2. Under Account Information, choose the IMAP/POP account that fails.
     3. Select Account Settings > Server Settings.
     4. Paste the new app password into the Password box.
     5. Select Next, then Done.
3. If on Windows 10 and using IMAP/POP, disable TLS 1.3 if present
   • This applies if Outlook shows errors like “The connection to the server was interrupted” or “Your server unexpectedly terminated the connection.”
   • Open Regedit (Start > type regedit > Enter).
   • Navigate to: Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols
   • If a TLS 1.3 key exists under Protocols:
     1. Right-click Protocols and select Export to back up the key.
     2. Delete the TLS 1.3 key and its subkeys.
     3. Restart Outlook; if still not syncing, restart Windows.
   • After this, the Protocols key should no longer show TLS 1.3.
4. If Outlook shows certificate-related errors
   • If the message mentions “There is a problem with the proxy server’s security certificate” or similar:
     • The certificate may be invalid, expired, not trusted, or not matching the server name.
   • For errors about an untrusted certificate (for example, “The security certificate is not from a trusted certifying authority”):
     1. In Internet Explorer (or legacy browser using the Windows certificate store), browse to the HTTPS URL of the mail or RPC server.
     2. When the certificate dialog appears, select Install Certificate.
     3. Choose Place all certificates in the following store.
     4. Select Browse > Trusted Root Certification Authorities > OK.
     5. Select Next > Finish > OK.
   • If the certificate name or validity dates are wrong, contact the mail or system administrator to correct the server certificate.
5. Check for third‑party add-ins blocking Outlook
   • Start Outlook in safe mode:
     1. Press Windows key + R.
     2. Type outlook.exe /safe and press Enter.
   • If Outlook connects in safe mode, disable third‑party COM add-ins:
     1. In Outlook, go to File > Options > Add-Ins.
     2. In Manage, select COM Add-ins > Go.
     3. Clear check boxes for third‑party add-ins.
     4. Restart Outlook normally and test.
   • If a browser add-in is interfering (for certificate/proxy errors), disable third‑party add-ons in Internet Explorer as described in the referenced article.
6. If connecting to on‑premises Exchange via a network device requiring certificates
   • If a load balancer or similar device is configured to require client certificate validation during SSL handshake, Outlook on Windows cannot use the Windows certificate store as a credential.
   • In this case, configure certificate-based or modern authentication according to Exchange guidance, or have the admin adjust the network device so Outlook can connect without client certificate enforcement at the network layer.

If these steps do not resolve the issue, contact the email provider or Microsoft support with exact error text from Outlook (including any error codes) for further diagnosis.

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References:

• Error when Outlook tries to connect to a server by using an RPC connection or an HTTPS connection: There is a problem with the proxy server's security certificate
• Outlook IMAP or POP server unexpectedly terminated the connection, and the server was interrupted
• Outlook can't connect to an Exchange server that uses certificate validation on a network device