C#发送邮件小程序（支持群发，附件）

在这里，主要使用了system.web.mail命名空间下的类，具体代码如下：

先新建win项目，再复制：

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Web;
using System.Web.Mail;
using System.Text;
using System.Text.RegularExpressions;

 

namespace SendMail
{
 /// <summary>
 /// Form1 的摘要说明。
 /// </summary>
 public class Form1 : System.Windows.Forms.Form
 {
  private System.Windows.Forms.RichTextBox richTextBox1;
  private System.Windows.Forms.Label fromlabel;
  private System.Windows.Forms.Label subjectlabel;
  private System.Windows.Forms.Label tolabel;
  private System.Windows.Forms.Button sendbtn;
  private System.Windows.Forms.TextBox frombox;
  private System.Windows.Forms.TextBox subjectbox;
  private System.Windows.Forms.TextBox tobox;
  private System.Windows.Forms.Button exitbtn;
  private System.Windows.Forms.OpenFileDialog openFileDialog1;
  private System.Windows.Forms.LinkLabel linkLabel1;
  private System.Windows.Forms.TextBox Attachmentbox;
  /// <summary>
  /// 必需的设计器变量。
  /// </summary>
  private System.ComponentModel.Container components = null;

  public Form1()
  {
   //
   // Windows 窗体设计器支持所必需的
   //
   InitializeComponent();

   //
   // TODO: 在 InitializeComponent 调用后添加任何构造函数代码
   //
  }

  /// <summary>
  /// 清理所有正在使用的资源。
  /// </summary>
  protected override void Dispose( bool disposing )
  {
   if( disposing )
   {
    if (components != null)
    {
     components.Dispose();
    }
   }
   base.Dispose( disposing );
  }

  #region Windows 窗体设计器生成的代码
  /// <summary>
  /// 设计器支持所需的方法 - 不要使用代码编辑器修改
  /// 此方法的内容。
  /// </summary>
  private void InitializeComponent()
  {
   this.frombox = new System.Windows.Forms.TextBox();
   this.fromlabel = new System.Windows.Forms.Label();
   this.subjectlabel = new System.Windows.Forms.Label();
   this.tolabel = new System.Windows.Forms.Label();
   this.subjectbox = new System.Windows.Forms.TextBox();
   this.richTextBox1 = new System.Windows.Forms.RichTextBox();
   this.sendbtn = new System.Windows.Forms.Button();
   this.tobox = new System.Windows.Forms.TextBox();
   this.exitbtn = new System.Windows.Forms.Button();
   this.openFileDialog1 = new System.Windows.Forms.OpenFileDialog();
   this.linkLabel1 = new System.Windows.Forms.LinkLabel();
   this.Attachmentbox = new System.Windows.Forms.TextBox();
   this.SuspendLayout();
   //
   // frombox
   //
   this.frombox.Location = new System.Drawing.Point(120, 32);
   this.frombox.Name = "frombox";
   this.frombox.Size = new System.Drawing.Size(152, 21);
   this.frombox.TabIndex = 0;
   this.frombox.Text = "";
   //
   // fromlabel
   //
   this.fromlabel.Location = new System.Drawing.Point(16, 32);
   this.fromlabel.Name = "fromlabel";
   this.fromlabel.Size = new System.Drawing.Size(72, 23);
   this.fromlabel.TabIndex = 1;
   this.fromlabel.Text = "from";
   //
   // subjectlabel
   //
   this.subjectlabel.Location = new System.Drawing.Point(16, 72);
   this.subjectlabel.Name = "subjectlabel";
   this.subjectlabel.Size = new System.Drawing.Size(64, 23);
   this.subjectlabel.TabIndex = 3;
   this.subjectlabel.Text = "subject";
   //
   // tolabel
   //
   this.tolabel.Location = new System.Drawing.Point(336, 32);
   this.tolabel.Name = "tolabel";
   this.tolabel.Size = new System.Drawing.Size(48, 23);
   this.tolabel.TabIndex = 4;
   this.tolabel.Text = "to";
   //
   // subjectbox
   //
   this.subjectbox.Location = new System.Drawing.Point(120, 72);
   this.subjectbox.Name = "subjectbox";
   this.subjectbox.Size = new System.Drawing.Size(408, 21);
   this.subjectbox.TabIndex = 2;
   this.subjectbox.Text = "";
   //
   // richTextBox1
   //
   this.richTextBox1.Location = new System.Drawing.Point(40, 160);
   this.richTextBox1.Name = "richTextBox1";
   this.richTextBox1.Size = new System.Drawing.Size(648, 248);
   this.richTextBox1.TabIndex = 3;
   this.richTextBox1.Text = "";
   //
   // sendbtn
   //
   this.sendbtn.Location = new System.Drawing.Point(488, 120);
   this.sendbtn.Name = "sendbtn";
   this.sendbtn.TabIndex = 4;
   this.sendbtn.Text = "send";
   this.sendbtn.Click += new System.EventHandler(this.sendbtn_Click);
   //
   // tobox
   //
   this.tobox.Location = new System.Drawing.Point(392, 32);
   this.tobox.Name = "tobox";
   this.tobox.Size = new System.Drawing.Size(296, 21);
   this.tobox.TabIndex = 1;
   this.tobox.Text = "";
   //
   // exitbtn
   //
   this.exitbtn.Location = new System.Drawing.Point(600, 120);
   this.exitbtn.Name = "exitbtn";
   this.exitbtn.TabIndex = 5;
   this.exitbtn.Text = "exit";
   this.exitbtn.Click += new System.EventHandler(this.exitbtn_Click);
   //
   // openFileDialog1
   //
   this.openFileDialog1.Multiselect = true;
   //
   // linkLabel1
   //
   this.linkLabel1.Location = new System.Drawing.Point(8, 104);
   this.linkLabel1.Name = "linkLabel1";
   this.linkLabel1.Size = new System.Drawing.Size(104, 16);
   this.linkLabel1.TabIndex = 6;
   this.linkLabel1.TabStop = true;
   this.linkLabel1.Text = "Add Attachment";
   this.linkLabel1.LinkClicked += new System.Windows.Forms.LinkLabelLinkClickedEventHandler(this.linkLabel1_LinkClicked);
   //
   // Attachmentbox
   //
   this.Attachmentbox.Location = new System.Drawing.Point(120, 104);
   this.Attachmentbox.Name = "Attachmentbox";
   this.Attachmentbox.Size = new System.Drawing.Size(264, 21);
   this.Attachmentbox.TabIndex = 7;
   this.Attachmentbox.Text = "";
   this.Attachmentbox.TextChanged += new System.EventHandler(this.textBox1_TextChanged);
   //
   // Form1
   //
   this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);
   this.ClientSize = new System.Drawing.Size(728, 454);
   this.Controls.Add(this.Attachmentbox);
   this.Controls.Add(this.linkLabel1);
   this.Controls.Add(this.exitbtn);
   this.Controls.Add(this.tobox);
   this.Controls.Add(this.sendbtn);
   this.Controls.Add(this.richTextBox1);
   this.Controls.Add(this.subjectbox);
   this.Controls.Add(this.tolabel);
   this.Controls.Add(this.subjectlabel);
   this.Controls.Add(this.fromlabel);
   this.Controls.Add(this.frombox);
   this.Name = "Form1";
   this.Text = "Form1";
   this.ResumeLayout(false);

  }
  #endregion

  /// <summary>
  /// 应用程序的主入口点。
  /// </summary>
  [STAThread]
  static void Main()
  {
   Application.Run(new Form1());
  }
  // validate mail expresion
  private bool checkEmail( string dataToCheck )
  {
  
   string reguEmail = @"/w+([-+.']/w+)*@/w+([-.]/w+)*/./w+([-.]/w+)*";
   return Regex.IsMatch( dataToCheck, reguEmail, RegexOptions.IgnoreCase );
  }

  private void sendbtn_Click(object sender, System.EventArgs e)
  {
   //convert to array
   string[]maillist = tobox.Text.Split(',');
   //trim string in maillist
   for(int i=0;i<maillist.Length;i++)
   maillist[i] = maillist[i].Trim();
   string Attachmentpath = openFileDialog1.FileName;
   //send all mails
   foreach(string tomail in maillist)
    SendMail(frombox.Text, tomail,Attachmentpath);
   
  }
  
  void SendMail(string frommail,string tomail,string Attachmentpath)
  {
   //whether mail expresion is valid
   if(checkEmail(frommail)&&checkEmail(tomail))
   {
    try
    {
     //initialize Mailmessage object
     MailMessage message = new MailMessage();
     message.Subject = subjectbox.Text;
     message.From = frommail;
     message.To = tomail;
     message.Body = richTextBox1.Text;
     //real send method
     message.Attachments.Add(new MailAttachment(Attachmentpath,MailEncoding.Base64));
     SmtpMail.Send ( message ) ;

     //show mail succeeded
　　    MessageBox.Show( "Email has sent to ->" + tobox.Text ) ;
    }
    catch(Exception er)
    {
     MessageBox.Show("error:"+er.Message);
    }
   }
   else
    MessageBox.Show("error:wrong email expresion!");
  }
  private void exitbtn_Click(object sender, System.EventArgs e)
  {
   Application.Exit();
  }

  private void linkLabel1_LinkClicked(object sender, System.Windows.Forms.LinkLabelLinkClickedEventArgs e)
  {
   openFileDialog1.ShowDialog();
   Attachmentbox.Text = openFileDialog1.FileName;
  }

  private void textBox1_TextChanged(object sender, System.EventArgs e)
  {
  
  }
 }
}

关键点：

1  首先使用验证输入的验证邮件格式是否正确，使用了正则表达式，还可以使用errorprovidor，不过我没用过。

2  使用MailMessage类，初始化它的几个属性，非常简单。具体详见msdn

3 使用MailMessage.Attachment.add()方法添加附件

4 今天第一次使用openfileDialogue，原来是要某个链接激活打开的。具体看代码。不过在实现多个附件的话，处理比较复杂，我就没用了。