It is possible to send a email subscriptions in Reporting Services to recipients that are outside the domain (on the internet). You would need to setup the following configurations:
First of all, you might receive the following error when the e-mail subscription is running:
Subscription Error: "The e-mail address of one or more recipients is not valid."
This error usually occurs when the SMTP server is not configured for "email relay". SMTP relay between the Reporting Services server and the SMTP server should be enabled.
Ones the replay has being configured, you might receive the following error:
Failure sending mail: The server rejected the sender address. The server response was: 550 5.7.1 Client does not have permissions to send as this sender
There are two more settings to configure apart from the Relay in the SMTP server:
Configuring a Report Server for E-Mail Delivery
2. If you want to configure the relay authenticated, you need to give “Send As” permissions Reporting Services account in the SMTP server. “Send As” allows one user to send an email as though it came from another user. More info:
How to Manually Grant Send As Permissions to a User with Full Mailbox Access
2. Create a receive connector to accept the anonymous relay and add the IP of the Reporting Services machine to the list of IPs of the connector.
Now you should be able to send emails outside the organization without errors
Reporting Services Support Engineer