Hello,
We need to use a mail (contact@domain.tld) alias that forwards mails to 2 or more ynh mailboxes.
A mailman mailing-list is not the solution because it should not be moderated.
It seems to be impossible : when the second user wants to define the same alias, an error message appears.
Thanks for your ideas 
Well, we have this on Yunohost’s infra, and basically what you want to do, I think, is :
The drawback, though, is that it still does not allow you to have Alice and Bob with alias contact (which means, for instance, that they won’t easily be able to send mails on behalf of “contact” from Roundcube/Rainloop/…). But at least emails sent to Contact will correctly be forwarded to Alice & Bob
Salut @LoJo,
J’ai l’impression que c’est ça que tu veux faire : Add a redirection mail/alias without attaching it to a YunoHost account