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A Secure Connection to the Server Cannot be Established on Microsoft Outlook

When you try to test your IMAP configured account there may be an instance where the following error message appears:

A secure connection to the server cannot be established.

Cause of the error in Microsoft Outlook

The error can be caused due to IMAP misconfiguration, modifications in the Windows Registry or even third-party software blocking the requests:

  • Third-party Antivirus: Antiviruses sometimes offer internet security which blocks such requests and you will have to whitelist your server
  • Modification of Ciphers or Protocols in the Windows Registry: Modifications made to the ciphers and protocols keys in the Windows Registry can also cause this and could be solved with a 3rd party utility
  • Incorrect IMAP Configuration: Using the wrong ports or encryption types, can also be the cause of the message in some cases.

Whitelist the Server in the Third-Party Antivirus

If you use a third-party anti-virus add the IMAP server to the whitelist. This may solve the issue in many cases.

Modifying Windows Registry

In other cases, the issue can be due to the modifications made to the ciphers and protocols entries in the Windows Registry. These entries are important for the function of the Secure Channel, also known as Schannel, security package. This package supports various encryption types such as SSL 2.0 and 3.0, TLS 1.0 etc. Modifications to such entries can often lead to various errors when it comes to the use of these encryption types.

You can fix this by using third-party software: Here are the steps:

  1. Download the IIS Crypto tool from www.nartac.com/Products/IISCrypto/Download.
  2. Install the program and launch it.
  3. In the Schannel tab, click Best Practices and hit Apply
  4. Restart your computer

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