"User not authenticated" error in Outlook Express

This article provides resolution to the error "User not authenticated" reported by users who can't send or receive e-mails when using an e-mail client especially Outlook Express.

Error:

The message could not be sent because the server rejected the sender's e-mail address. The sender's e-mail address was 'xxxxxxx@hotmail.com'. Subject 'xxxxx', Account: 'Hotmail', Server: 'smtp.live.com', Protocol: SMTP, Server Response: '550 5.7.3 Requested action aborted; user not authenticated', Port: 587, Secure(SSL): Yes, Server Error: 550, Error Number: 0x800CCC78

Resolution:

Make sure that the "My server requires authentication" option is enabled.

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