When login to Tuleap using
http://my-tuleap.website.me directly from the homepage login (ie: not using top-right corner "login" option :
https://my-tuleap.website.me/account/login.php ) then mailman URLs are not available - since the configuration file /etc/httpd/conf.d/mailman.conf is not included from /etc/httpd/conf/httpd.conf (but it is included from /etc/httpd/conf/ssl.conf).
The only way to access mailman URLs is https://.
Note the malfunctioning URLs are mentioned within mailman notifications emails too !
I think a choice should be made here : either configure the system so Tuleap can only be accessed with https:// links, or review apache configuration files.