The content of the error message itself may vary according to the email client. The error number 0x800CCC79 is shown in the error message received when using Outlook Express and Windows Live Mail. With Outlook Express you will get something like this:
The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was 'firstname.lastname@example.org'. Subject 'anything', Account: 'servername.com', Server: 'servername.com', Protocol: SMTP, Server Response: '550 relay not permitted', Port: 465, Secure(SSL): Yes, Server Error: 550, Error Number: 0x800CCC79
With Windows Live Mail the message is almost the same:
The message could not be sent. The authentication setting might not be correct for your outgoing e-mail [SMTP] server. For help solving this problem, go to Help, search for "Troubleshoot Windows Live Mail", and read the "I'm having problems sending e-mail" section. If you need help determining the proper server settings, please contact your e-mail service provider.
The rejected e-mail address was 'email@example.com'. Subject 'anything' Server Error: 550 Server Response: 550 relay not permitted Server: 'servername.com' Windows Live Mail Error ID: 0x800CCC79 Protocol: SMTP Port: 465 Secure(SSL): Yes
In this case the error number (0x800CCC79) and the server response (550 relay not permitted) show what the problem actually is. The reason is that you have probably forgotten to enable SMTP server authentication, and it is required in order to send emails. Just open the properties window for the particular email account and from the outgoing server options mark the checkbox labeled My outgoing server requires authentication.
The solution is the same for Microsoft Outlook. There, however, you won't receive the same error message when sending an email. Instead, with Outlook 2002, Outlook 2003, and Outlook 2007 initially it will appear is if the message is sent, but it won't be received by the recipient. You'll receive a bounce-back “Undeliverable” message in the local inbox of the email client. It's content looks like this:
Your message did not reach some or all of the intended recipients. Subject: anything Sent: 10/2/2011 11:06 AM The following recipient(s) cannot be reached: 'firstname.lastname@example.org' on 10/2/2011 11:06 AM 550 relay not permitted
When you configure email account options in Outlook 2010, the application always tests them before you can close the options window. If the same problem is present (disabled SMTP authentication), you'll receive a message that actually has a different error number:
Send test e-mail message: An unknown error occurred, error code: 0x80040607
The solution, however, is the same: after you open the settings window for the particular account, click on the More Settings button, then on the Outgoing Server tab, and mark the checkbox labeled My outgoing server (SMTP) requires authentication.
If you need help with finding the particular option for enabling SMTP authentication, or with configuring a particular email client, visit the respective article or tutorial.