You can use the SmarterMail Free License for Incoming and Outgoing Gateways, including Backup MX. We have three incoming Gateways, one of which is a Backup MX all using the Free License serving our primary installation which uses an Enterprise License.

I suspect what may be happening is that you have the card "Enable SmarterMail Gateway Mode" enabled in your SETTINGS > GATEWAYS/FAILOVER on your Backup MX. If this option is enabled then the inbound gateway will check with the primary mail server to determine if a recipient email address is valid. If the primary mail server is down it obviously cannot do this and will result in the 'rsp: 550 Mailbox Unavailable' or 'rsp: 550 No Such User Here' NDRs that you are reporting. Turning this setting off should allow for it to work properly when Backup MX is selected for the Gateway Mode.

Hello, 

Thank you for reaching out to the community. 

Please verify that you have gateway mode enabled. 

1. Log in to SmarterMail on the backup MX as a system administrator.
2. Navigate to Settings>Gateways/Failover>Incoming Gateways.
3. Click New, and select Backup MX in the Gateway Mode field.
4. Configure the additional fields here including the IP address of the backup MX and any spam settings. Save when complete. 

Please let me know if this helps. 

Kind Regards, 

Scarab, thanks for the response. I read your reply, then the guide again, then looked at the config, now I think the guide may be wrong? 

The guide says:

1. Log in to SmarterMail on the backup MX as a system administrator.
2. Navigate to Settings > Gateways/Failover > Incoming Gateways.
3. Click New, and select Backup MX in the Gateway Mode field.
4. Configure the additional fields here including the IP address of the backup MX and any spam settings. Save when complete.

That doesn't seem right? On the "backup" MX system, shouldn't I set that uip in the "Outgoing" gateway, and not the incoming one?  

In my current config, on my Backup MX, I have my Primary MX configured under Settings > Gateways/Failover > Inbound Gateways. This seems incorrect? But this is what the guide says.

@ Zach, again I am confused. In step 4, when you say "including the IP address of the backup MX and any spam settings.", does that mean you want me to put in the IP of the backup mx ITSELF in this field (as system admin on the backup MX server).