You sated that you have created a send connector, if you are allowing a relay through then you want to create a receive connector.
You can use these instructions but I suggest you at least secure it to just the IPs of the servers you control.
To create a Receive connector on a computer that has the Edge Transport server role installed, select Edge Transport, and then in the work pane, click the Receive Connectors tab.
To create a Receive connector on a Hub Transport server role, in the console tree, expand Server Configuration and select Hub Transport. In the result pane, select the server on which you want to create the connector, and then click the Receive Connectors tab.
In the action pane, click New Receive Connector. The New Receive Connector wizard starts.
On the Introduction page, follow these steps:
In the Name field, type a meaningful name for this connector. This name is used to identify the connector.
In the Select the intended use for this Receive connector field, select Custom.
On the Local Network settings page, follow these steps:
Select the existing All Available IPv4 entry, and then click Remove icon.
Click Add. In the Add Receive Connector Binding dialog box, select Specify an IP address. Type an IP address assigned to a network adapter on the local server that's best able to communicate with the remote messaging server. In the Port field, type 25, and then click OK. Leave the Specify the FQDN this connector will provide in response to HELO or EHLO field blank.
On the Remote Network settings page, follow these steps:
Select the existing 0.0.0.0 - 255.255.255.255 entry, and then click Remove icon.
Click Add or the drop-down arrow located next to Add and type the IP address or IP address range for the remote messaging server or servers that are allowed to relay mail on this server. When you're finished entering the IP addresses, click OK.
On the New Connector page, review the configuration summary for the connector. If you want to modify the settings, click Back. To create the Receive connector by using the settings in the configuration summary, click New.
On the Completion page, click Finish.
In the work pane, select the Receive connector that you created.
Under the name of the Receive connector in the action pane, click Properties to open the Properties page.
Click the Permission Groups tab. Select Anonymous users.
Click OK to save your changes and exit the Properties page.