在用NMSMTP控件发送邮件时,如何解决SMTP服务器需要身份验证问题.(50分)

IDMessage1.Subject := ...//主题
IDMessage1.Recipients.EMailAddresses := ... //收件人
IDMessage1.CCList.EMailAddresses := ...  //抄送
IDMessage1.BccList.EMailAddresses := ...  // 副本
IDMessage1.From.Address := ... //发件人
IDMessage1.Body.Clear;
IDMessage1.Body.Assign(Memo1.Lines);  //邮件正文
for i := 0 to ListBox1.Count - 1 do
  TIdAttachment.Create(IDMessage1.MessageParts,ListBox1.Items[i]); //附件
IDSMTP1.Send(IDMessage1);