Comment 2 for bug 1170726

BCC is the whole point of this bug. If a list requires 'explicit destination', the list address or an acceptable alias must be in the To: or Cc: headers of the message. The bug says acceptable aliases aren't checked and it means against the To: or Cc: headers.

Checking against the envelope recipient is irrelevant since if the list weren't the envelope recipient of the message, the list's chain wouldn't be seeing the message in the first place.