When I install sympa, it looks well, and goes correctly on. But it does absolutely nothing : with -d option, I just see Reaper unwaited pids : Open = 0 ad infinitum and no messages adressed to sympa seems to come in. The messages are not even in the spool/msg directory.

Solution : verify the setuid bit on program queue :

rwsr-xr-x   1 sympa    sympa      40012 juin 30 15:44 queue
 

Explanation : you probably (and prudently) compile and install sympa as a normal user (sympa perhaps ? ), but user root is the only one authorized to modify setuid bit. You may compile with a normal account, but don't forget to modify manually the setuid bit on $sympa/bin/queue