How do I set my Mailman list to never hold anything for moderator approval?

Implicit destination / Too many recipients

Mail which is bcc'ed to the list (or is sent to another list which has your list as a member), or has a large number of recipients, will be held. When Mailman holds a message like this for moderator approval, the reason is "Message has implicit destination" or "Too many recipients to the message". To turn these off:

1. Go to Privacy Options > Recipient Filters.
2. Change the setting for "Must posts have list named in destination (to, cc) field (or be among the acceptable alias names, specified below)?" to No
3. Change the setting for "Ceiling on acceptable number of recipients for a posting" to 0.

source: http://kb.mit.edu/confluence/pages/viewpage.action?pageId=11337854