How to Enable Anonymous Access for an SMTP Connector
After you have configured the settings for an SMTP connector, you must enable anonymous access for outbound SMTP connections. This is because other servers receiving your organization's outbound mail will expect your SMTP server to connect anonymously.
Procedure
To enable anonymous access
In the Properties dialog box for your SMTP connector, on the Advanced tab, click Outbound Security.
In the Outbound Security dialog box, select Anonymous access. See the following figure.
Outbound Security dialog box