Séverin,
The problem is sometimes, you make comments to a contribution without committing anything and no mail is then sent.
IMHO, the solution would be to have an option to get via mail any comment on a contribution you participate to, a bit like the way it is on the tracker, where you can choose to "watch" an issue and get notified about changes about it. This option should be enabled by default for the contributor and maintainer when a contribution is proposed, so that they get any comments about it.
One could imagine too that any AMOS user could add/remove herself to the "watchers" of any contrib, to get (or not to get) notified too.
Does it make sense to someone else?
PS. Thanks for creating the issue on the tracker.
Nicolas