Exchange 2007 I have a remote web server (see here for more info http://learn.iis.net/page.aspx/624/application-pool-identities). The application pool is running with the NETWORKSERVICE account on the remote system. I understand that NETWORKSERVICE would be the account that would be used to access network resources. I'm assuming that means in a domain-joined environment, any kind of authentication to remote service (like Exchange) would happen with that NETWORKSERVICE account? Oddly, Exchange doesn't seem to be recording any information... Nothing! But on the application server, I'm seeing the following in the application Event Viewer log (created by the application that's failing): "Mailbox unavailable: The server reponse was: 5.7.1 Client does not have permissions to send as this sender at System.NET.Mail.MailComment.CheckResponse(..."

Hello Marco, Are you able to send or receive mails from that application? As you said there are not events getting generated on exchange related to Network Authentication or any error related to the application. I am sure you must have been checked the permission on that Mailbox for NetworkService. Gulab | MCITP: Exchange 2010-2007 | Skype: Gulab.Mallah | Blog: www.ExchangeRanger.Blogspot.com

How does one configure access to a mailbox to the NETWORKSERVICE account on a remote server? I'm not sure how to accomplish this, but maybe I need to do some more research.

Hi, What's your application used for? If you want the application to send a message through the exchange server, you need to allow the relay for the application server or sending the message by authentication. Allow Anonymous Relay on a Receive Connector http://technet.microsoft.com/en-us/library/bb232021.aspx For sending a message by authentication, please refer the following C # code: SmptClinet mySMTP= new SmtpClient (servername, 25) System.Net.NetworkCredential user1= new System.Net.NetworkCredential ("user@domain.com", "Password"); mySMTP.Crendetial=user1 Gen Lin Forum Support Please remember to mark the replies as answers if they help and unmark them if they provide no help. If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com.