Hello Geoff, can we have you try removing the outgoing gateway routing, and then implement it one more time? I'm wondering if we give it another go if the settings might "stick" this time around. You may have luck checking the system or domain settings XML files as well to ensure the outgoing gateway routing is in fact detailed here. Lastly, check your Delivery/SMTP logs to see if SmarterMail might have had any trouble reaching the gateway machine as this can cause us to failover to the default IP address for sending as well. Let me know how you do!