On Fri, 03 Jul 2015 06:50:58 -0700, you wrote:
$prefix/archives and the private/ and public/ sub-directories thereof are created on installation, and if Mailman is running there must be a 'mailman' site list and thus $prefix/archives/private/mailman/ and $prefix/archives/private/mailman.mbox/ subdirectories whether or not they contain any actual archives.
Further, If $prefix/archives/private didn't exist, check_perms would have thrown a "OSError: [Errno 2] No such file or directory:" exception instead of reporting it was o+x.
Interesting: My $prefix is /usr/lib/mailman. However, there is a /var/lib/mailman as that's where archives is. It's owned and grouped properly, and it does have the 1-bit set in the 'other' portion of its permissions mask. I can definitely fix that. But why does this all appear in /var/lib/mailman and not /usr/lib/mailman?