验证exchange服务器上的电子邮件地址

我允许用户管理存储在数据库中的通讯组列表。用户只允许输入@mydomain.com的电子邮件。然后,一个基于web的应用程序获取通讯组列表并发送电子邮件。在从应用程序发送电子邮件之前,我想验证电子邮件是否有效。

    Dim SendTo As String = "ThisIsNotARealEmailAddress@mydomain.com"
    Dim SentFrom As String = "me@mydomain.com"
    Dim MessageBody As String = "blah blah blah"
    Dim MessageSubject As String = "This is the subject"


    Dim mm As New MailMessage(SentFrom, SendTo)
    mm.Subject = MessageSubject
    mm.IsBodyHtml = False
    mm.Priority = MailPriority.High
    mm.Body = MessageBody

    Dim smtp As New SmtpClient()
    smtp.Send(mm)

如果SendTo不是有效的电子邮件地址,服务器将返回以下错误:

Mailbox unavailable. The server response was: 5.1.1 <ThisIsNotARealEmailAddress@mydomain.com>... User unknown

try catch 发送电子邮件时阻止?