### 2.7.3 Recipient Filters

The variables in this section control various filters based on the recipient of the message.

require_explicit_destination
  This controls whether the mailing list posting address must be explicitly named in the To: or Cc: recipient lists. The main reason why it wouldn't is if the message was blind-carbon-copied (i.e. Bcc:'d) to the list. Spammers like to do this, but sometimes legitimate messages are forwarded to the list this way.

  If the list is not explicitly addressed and this setting is turned on, the message will be held for moderator approval.

acceptable_aliases
  This is the list of alternative addresses that are acceptable as a list posting address when `require_explicit_destination` is enabled. This is useful for when there aliases for the main posting address (e.g. `help@example.com` may be an alias for `help-list@example.com`).

max_num_recipients
  This is the maximum number of explicit recipients that are allowed on the posted message. Spammers sometimes send messages with lots of explicit recipients, so setting this number to a reasonable value may cut down on spam.