.NET SMTP Client - Client does not have permission

Question

I'm getting strange occurance on our servers when I am trying to send an email using SmtpClient class via an ASP MVC3 project. This is the code I am using.

try
{
    var client = new SmtpClient("MailServer");
    client.UseDefaultCredentials = true;

    MailMessage message = new MailMessage("[e-mail]", "[e-mail]", "Test Message", "Test Body");
    client.Send(message);
}
catch (Exception ex)
{
    // Do Nothing
}

I have deployed on three environments; on Windows 7 (using VS 2010 IIS) it sends the email fine, on the Windows 2003 IIS6 machine it sends the email fine, finally on the Windows 2008 R2 II7 server I get the following error:

Mailbox unavailable. The server response was: 5.7.1 Client does not have permissions to send as this sender using username 

Can anybody advise on what may be causing this. I have noticed that when I view User.Identity.Name, this is returning an empty string.

Answer 1

What does User.Identity.IsAuthenticated return, if it returns false that is your problem. You are trying to send mail as an unauthenticated user.

Answer 2

Had the same issue - the credentials from ASP.Net were never going to be something that could send e-mail in my environment. So I figured out this path through the mess (which also includes the possibility that NTLM doesn't always work right and that I was putting the mail configuration info in web.config):

System.Net.Configuration.SmtpSection section = ConfigurationManager.GetSection("system.net/mailSettings/smtp") as System.Net.Configuration.SmtpSection;

// set up SMTP client
SmtpClient smtp = new SmtpClient();
System.Net.CredentialCache myCache = new System.Net.CredentialCache();
NetworkCredential myCred = new NetworkCredential(section.Network.UserName, section.Network.Password);
string host = section.Network.Host;
int port = section.Network.Port;

// do this because NTLM doesn't work in all environments....
if (myCred != null)
{
    myCache.Add(host, port, "Digest", myCred);
    myCache.Add(host, port, "Basic", myCred);
    myCache.Add(host, port, "Digest-MD5", myCred);
    myCache.Add(host, port, "Digest MD5", myCred);
    myCache.Add(host, port, "Plain", myCred);
    myCache.Add(host, port, "Cram-MD5", myCred);
    myCache.Add(host, port, "Cram MD5", myCred);
    myCache.Add(host, port, "Login", myCred);

    //myCache.Add(host, port, "NTLM", myCred);
}
smtp.Credentials = myCache;
smtp.UseDefaultCredentials = false;
//smtp.EnableSsl = true;

Depending on your configuration, you might need to uncomment the last line.

Answer 3

I solve this problem removing authentication credentials from web.config

<system.net>
<mailSettings>
  <smtp from="[e-mail]">
    <!--network host="EXCH-SERVER" port="25" userName="userName" password="password" defaultCredentials="false" /-->
    <network host="EXCH-SERVER" port="25" />
  </smtp>
</mailSettings>

Answer 4

It is likely that the mail server does not support sending anonymous emails and will require credentials to be specified which are registered on the mail server.

You can specify the credentials like so:

client.UseDefaultCredentials = false;
client.Credentials = new System.Net.NetworkCredential("username", "password");

Hope this helps.

Answer 5

If you have try everything and it is still failing, one possibility is that the server accept only anonymous user. If you try to connect with credentials:

• defaultCredentials="true"
• defaultCredentials="false" userName="foo" password="false"

Then the server WILL return the error .NET SMTP Client - Client does not have permissions to send as this sender.

That's weird, but as a last resort, just try the simple:

• defaultCredentials="false"

Answer 6

One thing worked for me using Visual studio 2013 running packages. i removed the 'Use Windows Authentication' tag in the SMTP Connection Manager Editor.