I did what this tutorial said:
And instead of inserting hash:/var/lib/mailman/data/virtual-mailman
in virtual_maps (because it wasn't working) I added it at the end of virtual_mailbox_maps.
I also added hash:/var/lib/mailman/data/aliases in alias_maps.
Everything goes fine, from postfix to mailman:
Jun 9 23:14:05 server postfix/virtual: 7BF7E8EDE325: to=<xxxxx@xxxx>, relay=virtual, delay=1, status=sent (delivered to mailbox)
But it's never actually delivered, still waiting on mailman to answer to the mail.