ASP.net发送Email(2)

下面是一个实际的例子，客户端在WinXP的Command窗口中通过"telnet smtp.263.NET 25"命令连接到263的smtp服务器发信：

220 Welcome to coremail System(With Anti-Spam) 2.1

EHLO 263.NET

250-192.168.30.29

250-PIPELINING

250-SIZE 10240000

250-ETRN

250-AUTH LOGIN

250 8BITMIME

AUTH LOGIN

334 VXNlcm5hbWU6

bXlhY2NvdW50

334 UGFzc3dvcmQ6

bXlwYXNzd29yZA==

235 Authentication successful

MAIL FROM:myaccount@263.NET

250 Ok

RCPT TO:myaccount@263.NET

250 Ok

Data

354 End data with <CR><LF>.<CR><LF>

This is a testing email.

haha.

.

250 Ok: queued as AC5291D6406C4

QUIT

221 Bye

上面的内容就是发信的全过程。其中与身份验证有关的主要是第九到第十四行：

AUTH LOGIN "客户端输入

334 VXNlcm5hbWU6 "服务器提示“Username:="

bXlhY2NvdW50 "客户端输入“myaccount="的Base64编码

334 UGFzc3dvcmQ6 "服务器提示“Password:="

bXlwYXNzd29yZA== "客户端输入“mypassword="的Base64编码

235 Authentication successful "服务器端通过验证

从上面的分析可以看出，在这个身份验证过程中，服务器和客户端都直接通过Socket传递经过标准Base64编码的纯文本。这个过程可以非常方便的用C#实现，或者直接添加到原有的源代码中。另外，有些ESMTP服务器不支持AUTH LOGIN方式的认证，只支持AUTH CRAM-MD5方式验证。但是这两者之间的区别只是文本的编码方式不同。

实现此功能的源代码可以在SourceForge.NET http://sourceforge.NET/projects/opensmtp-net/ 上找到下载。下面给出了一个简单的伪码：

public void SendMail(MailMessage msg)   

{  

NetworkStream nwstream = GetConnection();

WriteToStream(ref nwstream, "EHLO " + smtpHost + "\r\n");

string welcomeMsg = ReadFromStream(ref nwstream);

// implement HELO command if EHLO is unrecognized.

if (IsUnknownCommand(welcomeMsg))

{

WriteToStream(ref nwstream, "HELO " + smtpHost + "\r\n");

}

CheckForError(welcomeMsg, ReplyConstants.OK);    

// Authentication is used if the u/p are supplied

AuthLogin(ref nwstream);

WriteToStream(ref nwstream, "MAIL FROM: <" + msg.From.Address + ">\r\n");

CheckForError(ReadFromStream(ref nwstream), ReplyConstants.OK);

SendRecipientList(ref nwstream, msg.To);

SendRecipientList(ref nwstream, msg.CC);

SendRecipientList(ref nwstream, msg.BCC);

WriteToStream(ref nwstream, "DATA\r\n");

CheckForError(ReadFromStream(ref nwstream), ReplyConstants.START_INPUT);

if (msg.ReplyTo.Name != null && msg.ReplyTo.Name.Length != 0)

{ WriteToStream(ref nwstream, "Reply-To: \"" + msg.ReplyTo.Name + "\" <" +

msg.ReplyTo.Address + ">\r\n"); }

else

{ WriteToStream(ref nwstream, "Reply-To: <" + msg.ReplyTo.Address + ">\r\n"); }



if (msg.From.Name != null && msg.From.Name.Length != 0)

{ WriteToStream(ref nwstream, "From: \"" + msg.From.Name + "\" <" +

msg.From.Address + ">\r\n"); }

else

{ WriteToStream(ref nwstream, "From: <" + msg.From.Address + ">\r\n"); }



WriteToStream(ref nwstream, "To: " + CreateAddressList(msg.To) + "\r\n");



if (msg.CC.Count != 0)

{ WriteToStream(ref nwstream, "CC: " + CreateAddressList(msg.CC) + "\r\n"); }

WriteToStream(ref nwstream, "Subject: " + msg.Subject + "\r\n");

if (msg.Priority != null)

{ WriteToStream(ref nwstream, "X-Priority: " + msg.Priority + "\r\n"); }

if (msg.Headers.Count > 0)

{

SendHeaders(ref nwstream, msg);

}



if (msg.Attachments.Count > 0 || msg.HtmlBody != null)

{

SendMessageBody(ref nwstream, msg);

}

else

{

WriteToStream(ref nwstream, msg.Body + "\r\n");

}



WriteToStream(ref nwstream, "\r\n.\r\n");

CheckForError(ReadFromStream(ref nwstream), ReplyConstants.OK);

WriteToStream(ref nwstream, "QUIT\r\n");

CheckForError(ReadFromStream(ref nwstream), ReplyConstants.QUIT);

CloseConnection();

}

private bool AuthLogin(ref NetworkStream nwstream)

{

if (username != null && username.Length > 0 && password != null && password.Length > 0)

{

WriteToStream(ref nwstream, "AUTH LOGIN\r\n");

if (AuthImplemented(ReadFromStream(ref nwstream)))

{

WriteToStream(ref nwstream, Convert.ToBase64String(

Encoding.ASCII.GetBytes(this.username.ToCharArray())) + "\r\n");

CheckForError(ReadFromStream(ref nwstream), ReplyConstants.SERVER_CHALLENGE);

WriteToStream(ref nwstream, Convert.ToBase64String(Encoding.ASCII.GetBytes(

this.password.ToCharArray())) + "\r\n");

CheckForError(ReadFromStream(ref nwstream), ReplyConstants.AUTH_SUCCESSFUL);

return true;

}

}

return false;

}

总结

本文介绍了.NET中三种不同的使用SMTP协议发送邮件的方法，其中第一种（使用SmtpMail类）方案能满足大部分基本的发送邮件的功能需求，而第二种（使用CDO组件）和第三种（使用Socket自己撰写SMTP类）方案提供更自由和完整的定制方法，比如他们都能实现第一种方案不能做到的通过带认证的SMTP服务器发送邮件的功能。

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