GoDaddy Administratively Denying Emails from being Sent

We have multiple pages that send asp.net web page forms to us via email that were working up until 11/27/07.  We have not made any changes to the aspx files that do the sending.  We get this error:

Mailbox name not allowed. The server response was: sorry, your mail was administratively denied. (#5.7.1)

 Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Net.Mail.SmtpException: Mailbox name not allowed. The server response was: sorry, your mail was administratively denied. (#5.7.1)

Source Error:

Line 52:         objSMTPClient.Credentials = CredentialCache.DefaultNetworkCredentials
Line 53:         objSMTPClient.DeliveryMethod = SmtpDeliveryMethod.Network
Line 54:         objSMTPClient.Send(objMailMessage)

And the code is attached.  Does anyone know of any changes that GoDaddy might have made recently, or have any other ideas as to what may be causing this?  Thanks!

Dim objMailMessage As New System.Net.Mail.MailMessage
        Try
            With objMailMessage
                .IsBodyHtml = True
                .From = New Net.Mail.MailAddress(strEmailFrom)
                .To.Add(strEmailTo)
                .Bcc.Add("******@yahoo.com")
                .Subject = strSubject
                .Body = strBodyEmail
            End With
 
            Dim objSMTPClient As New System.Net.Mail.SmtpClient("relay-hosting.secureserver.net", 25)
            objSMTPClient.Credentials = CredentialCache.DefaultNetworkCredentials
            objSMTPClient.DeliveryMethod = SmtpDeliveryMethod.Network
            objSMTPClient.Send(objMailMessage)
            lblMessage.Text = "Farriintaada waa la diray.<br />"
        Catch ex As Exception
            lblMessage.Text = "Email not sent. " & ex.ToString
        End Try

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