.NET为什么我不能重写web.config邮件设置?

通常,我的应用程序发送带有通用系统地址的电子邮件。但在某些情况下,我希望以登录用户的身份发送。

Web.CONFIG:

<?xml version="1.0"?>
<configuration>
    ...
    <appSettings>
        ...
        <add key="DefaultEmailAddress"
             value="noreply@example.com" />
    </appSettings>
    <system.net>
        <mailSettings>
            <smtp>
                <network host="servername"
                         port="25"
                         userName="noreply"
                         password="apple" />
            </smtp>
        </mailSettings>
    </system.net>
    ...
</configuration>

此代码无法覆盖web.config中的默认发件人:

Dim from As String = ConfigurationManager.AppSettings("DefaultEmailAddress")
Dim to As String = "sadams@example2.com"
Dim m As New Mail.MailMessage(from, to)
m.IsBodyHtml = True
m.Subject = "Test"
m.Body = "<p>This is a test.</p>"

Dim c As New System.Net.Mail.SmtpClient

If CurrentUser.HasExchangeCredentials Then
    Dim userName As String = CurrentUser.ExchangeUserName
    Dim password As String = CurrentUser.ExchangePassword
    Dim address As String = CurrentUser.EmailAddress
    c.UseDefaultCredentials = False
    c.Credentials = New System.Net.NetworkCredential(userName, password)
    m.Sender = New Mail.MailAddress(address)
End If

c.Send(m)

我的电子邮件发出了,但它是作为 noreply@example.com网站 也不会显示在我的Outlook发送文件夹中。

我不想 使用默认凭据 . 我想用一个新的,不同的 网络凭据 .

我正在使用Microsoft Exchange。