Require Explicit Destination
The require_explicit_destination sets whether the list name must be in the destination field (to or cc) for Mailman to forward the message to the list. Since this is one of Mailman's spam controlling options, it is recommended this be set to yes.
The acceptable_aliases option allows you to set other addresses Mailman will accept as well as the list name. This can be of use if you bounce messages to the list or if the list is a member of another list. For instance, if NP_Toyshop was a member of NP_Toyshop_Announce, adding that list name to the acceptable aliases here would let Mailman know to accept those messages as though they had been directly addressed to NP_Toyshop.
Max Num Recipients
The max_num_recipients option allows you to set a maximum number of recipients Mailman will accept. Any amount exceeding this number will cause the mail to be held for moderation. This is another spam controlling option, as spammers often will have a large list of recipients to an email.