I am seeing a lot of emails, not making it to the list, due to
* having attachments (even small ones in footer).
* having the emails sent from addresses that are not members of the list.
I think that ATM Aymeric is working on allowing the approval of emails
by list admins, in the lurk web interface. Yet currently it is not possible.
So, in a nutshell dont add attachments to emails sent to the list.