Mailman 3.2.2 has been out since March: https://mailman.readthedocs.io/en/latest/src/mailman/docs/NEWS.html Mailman also officially supports python-3.7 so we should add this to the PYTHON_COMPAT list in the ebuild. The ebuild does not require any other modifications in order to build and run succesfully.
This package has an RDEPEND of dev-python/importlib_resources[${PYTHON_USEDEP}] However importlib_resources is now built into python3_7 and the importlib-resources packages may be redundant: https://importlib-resources.readthedocs.io/en/latest/ "importlib_resources is a backport of Python 3.7’s standard library importlib.resources module for Python 2.7, and 3.4 through 3.6. Users of Python 3.7 and beyond are encouraged to use the standard library module, and in fact for these versions, importlib_resources just shadows that module." So this dependency is probably not valid for python3_7 or newer.
The importlib_resources issue is a bit more complicated to fix, see also: https://gitlab.com/mailman/mailman/-/issues/690
To have at least some progress here I've committed a 3.3.0 ebuild. While it's in theory compatible with python 3.7 I can't set PYTHON_COMPAT yet due to missing dependencies.
Fixed
