This is a server error, not one with your PC. It could very well be a wrong setting however, such as using a wrong account.
Better contact your ISP to check the settings together.
Hope this helps.
After reformatting my Dell Dimension 4600 XP, Outlook Express won't send. I get 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 'Emailing: 19911123', Account: 'mail.wildblue.net', Server: 'mail.wildblue.net', Protocol: SMTP, Server Response: '554 <75-107-177-188.cust.wildblue.net[220.127.116.11>: Client host rejected: Access denied', Port: 25, Secure(SSL): No, Server Error: 554, Error Number: 0x800CCC79 I checked the ISP for spamware etc. and found nothing.Any help would be greatly appriciated. Thanks