Hi,
I noticed, CMake project uses reCAPTCHA
https://www.google.com/recaptcha/intro/invisible.html
with their installation of Mailman.
See bottom of this page
https://cmake.org/mailman/listinfo/cmake
Would it be practical to use it for OSGeo lists too?
Best regards,
--
Mateusz Loskot, http://mateusz.loskot.net