I expect the mail traffic to stay small (a dozen of emails, each less than 20Kbytes of HTML, each day). I do know that the Web traffic is small also (refpersys.org gets just a hundred HTTP requests per day).
We absolutely need that list to be publicly visible on the web, and we really use HTML emails, not plain text ones. AFAIK, this rules out both mailman and sympa. And I am not familiar with Python or Perl (even if I did learn many programming languages and even developed GCC MELT, a Lispy dialect to extend GCC in the past).
A typical email on that list would be refpersys.org/refpersys-Qt-based-GUI-mail-2019dec19.html; I extracted that manually from the thunderbird
I am capable of compiling a mailing list server program coded in C++, Go, C, ... etc. But even listmonk does not seem to accept HTML5 messages.
I could develop one myself in C++ (using Vmime + myhtml + some FastCGI library) or Go (improving nanolist or listmonk) perhaps under GPLv3+ license, but that would take me a week or two. I prefer devoting that time to RefPerSys.
Do you know other open source mailing list manager software compatible with HTML5 emails, e.g. Guile based? I am quite familiar with Guile.
I am very reluctant to use Google Groups, because several academics which could be interested by RefPerSys are hostile to Google (and as a French citizen and free software activist member of April, I tend to understand their position)
I could use framalistes.org/sympa (I regularly donate a few dozen of euros to them) but sympa is not friendly with HTML5 emails.
I care a lot about cybersecurity, since by day I am supposed to be a cybersecurity expert (since professionally developing tools like bismon)