[Mailman-Users] problem... User unknown

[Xavier NOEL LARDIN]

So, i have intalled Mailman on a server (redHat). I use sendmail for my MTA, and Apache for my web server.
the problem is when i send a message to an existant list, i have tle following message : User unknown !
I have tested this in few lists, and i obtain the same result !
Nowever, when i add member to my list, this person receive correctly the welcoming message.
So can you help me please.

Thanks