502 Bad Gateway openresty to SmarterMail.

[Tech1UAE]

Hi all,

I have installed Ubuntu Server 24.04.3 on a 4GB VM in Hyper-V. I installed SSH, logged in through a MacOS terminal and have installed Docker plus NGinx Proxy Manager. Everything works well and the web page loads. I've set up a couple of domains, the hosts work and the certs are downloaded fine.

I have two separate devices I need to route traffic to on ports 80 and 443. One is a Synology server running a WordPress installation for a website and the other is a SmarterMail installation running IIS for a number of email domains.

When I port forward direct to the SmarterMail, everything works fine but obviously, the NAS won't respond to any requests. When I set the port forward to the NPM, the NAS works great but I get a '502 Bad Gateway openresty' web error going to the IIS Windows Server 2022 Standard server.

I'm sure I'm missing something basic in IIS, maybe TLS or something like that? Does anyone have any suggestions?

Many thanks!