Onyeibo Oku writes:
Mailman starts well from virtual environment though, ... but systemd doesn't replicate that success.
systemd doesn't know anything about venv. If it's possible to source (not call as a command!) the venv bin/activate script via systemd, that should fix it. If not, we'll have to figure out what it is that the venv provides that the current systemd config does not. I would guess that after sourcing the venv's bin/activate
echo PATH: $PATH echo -n 'sys.path: '; python -c 'import sys; print (sys.path)'
will tell you what you need to know. You will have to translate sys.path into the form that is appropriate for PYTHON_PATH (I believe that's colon-separated, like PATH), and then tell systemd to set those environment variables. I can't help with that, I know nothing about systemd configs.
Steve