Not tested, but could be possible.
By default, checkmk uses postfix as mta.
- set postfix config outside of the container if possible (env vars should possible) as smarthost
- set your smtp-server
Easiest setup should be option2 (direct send), microsoft offers 3 in summary… google helps…
Not secure etc. only for test… how i said, not self tested or try to set it up like this…