How do I send emails outside my domain with Exchange 2007 and c#

Question

I am able to send emails using the typical C# SMTP code across Exchange 2007 as long as both the from and to addresses are within my domain.

As soon as I try to send ema

Answer 1

Authenticate to the exchange server.

http://msdn.microsoft.com/en-us/library/system.net.mail.smtpclient.credentials.aspx

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DefaultNetworkCredentials returns empty strings for username etc and causes this exception...

Here is an example, and here is another of sending authenticated message with System.Net.Mail.