Comment 4 for bug 266389

Originator: NO

So the message is held for implicit destination which means two things:

1) It passed your accept_these_nonmembers test.

2) It was held because Privacy Options...->Recipient
filters->require_explicit_destination is Yes and the list posting address
or another address in the acceptable_aliases list was not found in any To:
or Cc: header of the post.