The sensitivity checking keywords set an upper limit on the sensitivity of messages that can be accepted by a channel. The default is sensitivitycompanyconfidential; messages of any sensitivity are allowed through. A message with no Sensitivity: header is considered to be of normal, that is, the lowest, sensitivity. Messages with a higher sensitivity than that specified by such a keyword is rejected when enqueued to the channel with an error message:
message too sensitive for one or more paths used
Note that the MTA does this sort of sensitivity checking at a per-message, not per-recipient, level: if a destination channel for one recipient fails the sensitivity check, then the message bounces for all recipients, not just for those recipients associated with the sensitive channel.