There are two more settings to configure apart from the Relay in the SMTP server:

With authentication:

Configure the option <SMTPAuthenticate> to 2 in the rsreportserver.config

file to specify that the report server connects to the remote SMTP server in an

authenticated way. More info:

Configuring a Report Server for E-Mail Delivery

http://msdn.microsoft.com/en-gb/library/ms159155(v=sql.105).aspx

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

http://technet.microsoft.com/en-us/library/bb125118(EXCHG.65).aspx

Anonymous:

Configure the option <SMTPAuthenticate> to 0. More info:

Configuring a Report Server for E-Mail Delivery

http://msdn.microsoft.com/en-gb/library/ms159155(v=sql.105).aspx

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.