发送邮件时:连接不到SMTP 大家帮忙进来看看!谢谢!

大家好,我用自己做的WEB程序向Foxmail邮件系统发送邮件
首先,我先用outlook express向设置好的Foxmail发送邮件,成功 (说明设置,连接是正确的)
接着,用自己做的程序向Foxmail发送邮件,却显示连接不到SMTP ??????
而老师检查代码也说是对的,到底是哪里出错了呢?
这是我的发送邮件的代码:
using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using WebApp.DBconn;
using System.IO;
using System.Web.Mail;

namespace EmailSys.Emailbox

public class MailSend : System.Web.UI.Page
{
protected System.Web.UI.WebControls.Label Label1;
protected System.Web.UI.WebControls.Label Label2;
protected System.Web.UI.WebControls.Label Label3;
protected System.Web.UI.WebControls.Label Label4;
protected System.Web.UI.WebControls.TextBox tbxReceiver;
protected System.Web.UI.WebControls.TextBox tbxSubject;
protected System.Web.UI.WebControls.TextBox tbxContent;
protected System.Web.UI.WebControls.Button btnSubmit;
protected System.Web.UI.WebControls.Button btnCancel;
protected System.Web.UI.WebControls.Label lblErrMsg;
protected System.Web.UI.HtmlControls.HtmlInputFile fileUp;
protected System.Web.UI.WebControls.Label lblTip;

private void Page_Load(object sender, System.EventArgs e)
private void btnSubmit_Click(object sender, System.EventArgs e)
{
MailMessage myMail=new MailMessage();
myMail.From =Session["UserName"].ToString()+"@swn.com";
myMail.To = this.tbxReceiver.Text;
myMail.Subject =this.tbxSubject.Text;
if(fileUp.PostedFile.FileName.Trim()!="")
{
myMail.Attachments.Add(new MailAttachment (fileUp.PostedFile.FileName));
}
myMail.Priority = MailPriority.High;
myMail.BodyFormat = MailFormat.Text;
myMail.Body=this.tbxContent.Text;
SmtpMail.SmtpServer="BB";
SmtpMail.Send(myMail);//发送邮件
Response.Redirect("Successful.aspx");
}

}

private void tbxContent_TextChanged(object sender, System.EventArgs e)
{

}

private void tbxSubject_TextChanged(object sender, System.EventArgs e)
{

}