...

I followed your suggestions but nothing change. I always have in my apache log :

78.xx.yyy.zzz - - [24/Mar/2016:14:17:36 +0100] "GET /listinfo HTTP/1.1" 404 504 "-" "Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Firefox/45.0"

And what is in Apache's error log at /var/log/apache2/lists-error.log corresponding to this 404 error?

This file is empty... such as lists-access.log...

What are the results of ls -la /usr/lib/cgi-bin/mailman/

~  ls -la /usr/lib/cgi-bin/mailman/ total 140 drwxr-xr-x 2 root list 4096 mars 22 20:26 . drwxr-xr-x 3 root root 4096 mars 19 2015 .. -rwxr-sr-x 1 root list 10200 avril 6 2015 admin -rwxr-sr-x 1 root list 10200 avril 6 2015 admindb -rwxr-sr-x 1 root list 10200 avril 6 2015 confirm -rwxr-sr-x 1 root list 10200 avril 6 2015 create -rwxr-sr-x 1 root list 10200 avril 6 2015 edithtml -rwxr-sr-x 1 root list 10200 avril 6 2015 listinfo -rwxr-sr-x 1 root list 10200 avril 6 2015 options -rwxr-sr-x 1 root list 10200 avril 6 2015 private -rwxr-sr-x 1 root list 10200 avril 6 2015 rmlist -rwxr-sr-x 1 root list 10200 avril 6 2015 roster -rwxr-sr-x 1 root list 10200 avril 6 2015 subscribe