SmtpException: Mailbox Unavailable When Sending From Web Page
If you are using the System.Net.Mail namespace to send mail from a web page and are using Exchange 2007, you may get the following error message: [SmtpException: Mailbox unavailable. The server response was: 5.7.1 Client does not have permissions to send as this sender].
My solution was to create a seperate recieve connector where the permission groups were set to Anonymous users as shown in the figure below:
Next, in the Network tab, in the list under Receive mail from remote servers… as shown in the graphic, I added the ip address of the server wanting to send mail. Generally I place the IP address of individual web sites in there. I also include developer machine IP’s as well if they are testing mail enabled apps.
Thats all there is to it.