这两天做了一个小PROJECT，大致是一个SERVER监控系统，如果发现某部SERVER有异常，发送EMAIL到相关手机，以便在非工作时间和节假日也能及时知道系统故障。

其中一个功能就是发送EMAIL。程序是这样的：

myMailMsg.To = "888888888@mobile.att.net";

myMailMsg.From = "support@medicalit.net";

myMailMsg.Subject = "server down";

myMailMsg.Body = "Please call StarLan to chen Database Server";

myMailMsg.BodyFormat = MailFormat.Text;

SmtpMail.SmtpServer="localhost";

SmtpMail.Send(myMailMsg);

本来是用外部的SMTP SERVER

SmtpMail.SmtpServer="smtp.XXX.com";

但后来发现由于DATA CENTER的FIREWALL原因，改用

SmtpMail.SmtpServer="localhost";

运行后系统提示错误信息：

Email Fail
Could not access ''CDO.Message'' object.
Here is the full error message output:
System.Web.HttpException: Could not access ''CDO.Message'' object. ---> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Runtime.InteropServices.COMException (0x8004020F): The server rejected one or more recipient addresses. The server response was: 550 5.7.1 Unable to relay for 12321323@mobile.att.net

检查SMTP SERVICE，正常，估计是权限设置问题。打开IIS ADMIN，右键点击SMTP VIRTUAL SERVER(默认SMTP虚拟服务器)，选择属性，在ACCESS(访问)中点RELAY(中继)，增加127.0.0.1。一路OK回去。

这时候再运行程序，邮件发送成功。