尝试使用SmtpClient从某些电子邮件地址发送时出错？

Question

尝试使用SmtpClient发送电子邮件时，我收到以下错误。

  

{＆＃34; SMTP服务器需要安全连接或客户端未经过身份验证。服务器响应是：5.7.57 SMTP;客户未通过身份验证，以便在MAIL FROM [DB6PR0501CA0021.eurprd05.prod.outlook.com]期间发送匿名邮件＆＃34;}

我已经加倍检查所有密码是否正确，并通过office365从每个帐户成功发送电子邮件。

关于为什么会发生这种情况的任何想法？

public void SendMail(string smtpServer,
                         string userAccount,
                         string password,
                         string emailFrom,
                         string emailTo,
                         string emailCC,
                         string bcc,
                         string subject,
                         string body,
                         bool useSSL,
                         int port = -1,
                         List<Attachment> files = null)
    {
        MailMessage mm = new MailMessage();

        mm.From = new MailAddress(emailFrom);
        foreach (var address in emailTo.Split(new[] { ";" }, StringSplitOptions.RemoveEmptyEntries))
            if (address != string.Empty)
                mm.To.Add(address.RemoveWhitespace());

        if (emailCC != null)
            foreach (var address in emailCC.Split(new[] { ";" }, StringSplitOptions.RemoveEmptyEntries))
                if (address != string.Empty)
                    mm.CC.Add(address.RemoveWhitespace());

        mm.Body = body;//.Replace("\n",@"<br />");
                       // if (imageId > 0 || mm.Body.Contains(@"</") || mm.Body.Contains(@"/>"))
        if (mm.Body.Contains(@"</") || mm.Body.Contains(@"/>"))
            mm.IsBodyHtml = true;
        else
            mm.IsBodyHtml = false;

        if (!string.IsNullOrEmpty(bcc))
            mm.Bcc.Add(bcc.RemoveWhitespace());

        // add attachments if present
        if (files != null)
            foreach (Attachment a in files)
            {
                mm.Attachments.Add(a);
            }

        SmtpClient SmtpMail = new SmtpClient();
        SmtpMail.Timeout = int.MaxValue;
       // SmtpMail.UseDefaultCredentials = false;

        SmtpMail.Credentials = new System.Net.NetworkCredential(
                                        userAccount,
                                        password);
        if (useSSL)
            SmtpMail.EnableSsl = true;
        SmtpMail.Host = smtpServer;
        if (port != -1)
            SmtpMail.Port = port;

        Utility.WriteDebugLine(true, "SmtpMailSend");
        SmtpMail.Send(mm);           

    }