We have an outbound gateway setup to our email encryption server. We had set the priority to "high" and modified specific domains to use that outbound gateway. Other domains were set to "none" for outbound gateway. This setup had been working without an issue for over a year.
This past weekend we added additional outbound gateways because we setup additional email encryption servers. They are set to priority all. We modified specific domains to use specific outbound gateways but left the other domains set to "None".
This morning we received reports from users of the domains with Outbound Gateway set to "None" that they were receiving Delivery Failure errors stating "relaying denied" with the error listing our mail servers IP address.
The private IP and public IP of our mail server is on the whitelist for SMTP and SMTP Auth Bypass.
Any advice on how to resolve this issue? Is this expected behavior?
I've temporarily setup a free smartermail server to use as an outbound gateway for the domains that do not need an outbound gateway. This resolved the relaying issue but now we have issues with emails from those domains ending up in junk mail due to the public IP of the gateway never before being used for email.