[Mailman-Users] Undeliverable emails!

[Genevieve Buri]

Hi everyone,

I'm currently trying to set up Mailman and I can't post to my lists.
That's what I'm getting :

There was a SMTP communication problem with the recipient's email
server.  Please contact your system administrator.
    < hostname #5.5.0 X-Unix; 69>

mailmanctl is started, I have the aliases in /etc/aliases, I did 
newaliases, I receive the confirmation when I subscribe to a list, it's 
just the posting...

I've been working on this for days, I'm kind of tired.
Thank you for your help

Genevieve Buri