Please never close a valid task due your arbitrary definition of activity. It's incredibly rude.
This is still an issue: https://lists.wikimedia.org/pipermail/wikimedia-l/2020-June/095067.html.
Seems current behavior to escape body lines starting with From was introduced in https://bugs.launchpad.net/mailman/+bug/266068/comments/11
Mailman3 using HyperKitty may have changed some things; at least cannot find a ticket in https://gitlab.com/mailman/mailman/-/issues