[Evolution] can not send mail

[williamheiland aol com]

Dear sir or Madam,
                   when I try to send my messages form my out-box, I receive this error message: Error while sending message mail from command failed. E6.1 Client Authentication required. Use ESMTP EHLO and Auth: Could some please tell me what this means, and to fix the error so I can send mail with my evolution mail program. I will be very grateful for any help.
Sincerely,
William Heiland