Hi @nfaction,
maybe I need to phrase it a bit differently:
to be able to send mails from the Kopano clients (WebApp, ActiveSync clients) nothing need to be changed in the configuration of kopano-spooler or the kopano_spooler container
if you want to change configuration in the mail container, then I suggest to check their docs (you already linked to
https://docker-mailserver.github.io/docker-mailserver/edge/config/security/understanding-the-ports/) and ask in their project if you encounter any issues sending mail for example through Thunderbird. In my eyes this is out of the scope of the kopano-docker project, but should be possible to achieve through configuration nonetheless.
running a second instance of docker-mailserver is not necessary
PS: why did you delete your topic regarding the use of linuxserver.io swag?