I noticed that certain emails sent to the group, which were absolutely legitimate end up not showing up in the group. You can verify this by going here:
If you don't see your message it means that it's "Pending" review. Unfortunately, we don't always get a notification about that, and we might have a case in which a message might take a while to show up (basically when I look at the moderation tool and see that there are messages, I just approve them). For example, Lucas' last email was in that state for a while for no apparent reason.
TL;DR: If you suspect your message isn't getting posted, please email me.
George