Thanks but…
As I explained, the sending of spooled messages works fine when restarting the spooler (at reboot notably).
The problem is that the same spooled messages are never sent before.
Actually there is nothing related in the crontab. I had a look at crontabgen and commented the removal of /tmp/crontab: there is code to generate the events what means spool them, OK this part works…
Then I’m looking for clues about how the spooler is made and how to make it flush periodically.
Thanks, Best regards.