I built a postfix relay several years ago that relays through office365. This is limited to hosts on the VPN, but now want to provide a public IP and allow remote printers to relay through postfix for send to email.
My issue is a lack of understanding of how to add smtp authentication for the printers to use without messing up the authentication for office365. I think this is purely a perspective issue.
The new postifix installation is running in Docker using the config found here https://github.com/juanluisbaptiste/docker-postfix and works just like my old install.
Looks like I just need to figure out getting saslauthd to run in the container. Then it should auth against pam using a local account.