Cannot send mail due to SMTP server error

I have setup windows mail with few pop3 accounts. Everything is done but now when I try to send email, it gets failed with the following error message:

The authentication setting might not be correct for your outgoing e-mail [SMTP] server.

The rejected e-mail address was '< username>@saber.net'. Subject 'Re: For <account>', Account: 'SaberNet', Server: 'smtp.saber.net', Protocol: SMTP, Server Response: '550 5.7.1 Access denied', Port: 25, Secure(SSL): No, Server Error: 550, Error Number: 0x800CCC78

Somebody please help me out.

I doubt your Antivirus programs for this error. Which Antivirus are you using? If it is Norton or McAfee than you will need to completely uninstall it from your system because both of these security suites contain Email Scanning feature that blocks your emails considering them as malicious. Even disabling this feature will not fix the problem. So just remove them and install AVG Free Edition. That has been named compatible with Windows Mail.

Thanks for your help Manik. As per your suggestion I uninstalled my Norton and installed AVG. But at the same a guy aso suggested me to change the SMTP server address to Comcast and remove Saber. Well I did the same and now I can send the email. Thank you very much.

People facing such problem can make these settings as well. The settings are from my PC and are working fine:

Launch Windows Mail, click Tools > Accounts > your email address > Properties. Now go to Advanced Tab and changed port 25 to Port 80. Now go to Servers Tab and makes sure the check box for “My server requires authentication” is checked marked. Click OK. Restart Windows Mail and try sending a new mail. It should work.