Client does not have permission to send as this sender

Question

We have a CRM web application hosted on a server. When a user launches the site, the site provides facility to the customer to send the query into the system using the email. The website provides the filed for the customer to enter customer’s email ID. The
customer email address is used by the system to send the response back.
We are doing a new implementation for SMTP authentication for the emails send into the contact center using a public website. The flow of the system to use the SMTP authentication is:
Customer launches the website.
Customer chooses to send the his/her query using the email from the website.
Website asks for the customer’s address, so that the query can be 
answered back to the provided email address say [email protected] .
We have an account configured on the MS-Exchange 2010 say [email protected]
So before sending the email the website system performs the SMTP Authentication using the credentials of [email protected]
Now the system creates the email MIME using the email address provided by the customer on the website i.e. say [email protected].
After successful SMTP authentication for the address   [email protected] system starts sending the email.
Here we are facing the issue:
While sending the email if the customer’s address is also configured on the same exchange used by the system i.e. exchange on [email protected] is configured
 then website system is able to relay or send the email.
If the customer’s address is not configured on the same exchange used by the system where [email protected] is configured then the system is not able to send the email it results into the error of: “Client
does not have permission to send as this sender [email protected].
In short if the website performs the  SMTP authentication then it requires the FROM address configured on the same exchange used for the smtp authentication in the email MIME from address.
Configuration tries:
As suggested on various forums and at Microsoft tech group we tried following things but no success:
Checked the checkbox “Authenticated Users”  selected “Accept any Sender”.
Created a new relay and given the IP of the machine hosting the website or trying to send the email
Run the command from the EMC “Exchange management console”
Add-AdPermission -Identity "Default Receive Connector" -User "NT AUTHORITY\Authenticated Users" -ExtendedRights ms-Exch-SMTP-Accept-Any-Sender.

Answer 1

You can create a new connector to which everything is permitted - eg New-ReceiveConnector -Name "Anonymous Relay" -Usage Custom -PermissionGroups AnonymousUsers -Bindings 10.2.3.4:25 -RemoteIpRanges 192.168.5.77