Hi,
I am using Windows XP Pro OS connecting to a mail server using linux in a centos flatform. Using Thunderbird as a client got me no problem in receiving and sending mails using but when I try to configure my email using Microsoft Outlook or Outlook Express I can not send mails and this error occurs.

The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was 'username@email.com'. Subject 'Sample Mail', Account: 'mail.account.com', Server: 'smtp.account.com', Protocol: SMTP, Server Response: '504 5.5.2 <walk2>: Helo command rejected: need fully-qualified hostname', Port: 25, Secure(SSL): No, Server Error: 504, Error Number: 0x800CCC79.

Please help me solving this problem.

Thanks

I'm guessing that you can take the error message literally. Your PC needs to present itself to the mail server with a fully qualified domain name and it's probably only using the hostname (usually the same as the netbios name in Windows). Make sure your Primary DNS suffix is set. Both on your network card properties or under the system control panel applet.