Please consider rephrasing parts of the text on communication as it is not entirely crystal clear in its current form. For starters, the examples mentioned in the header (e.g. an alert that was sent to a responsible provider, a public health agency that was notified about a reportable condition.) are both in past tense - is there a certain reason for that? Can't a Communication concern a future or present message?

I would suggest to change the intro from : "This resource is a record of a communication even if it is planned or has failed." to "This resource is a container/conveyance of communication between parties". In an introduction I find it a little irrelevant whether it is planned, failed or succeeded - that is a matter of context, timing and interpretation. 

See also https://chat.fhir.org/#narrow/stream/179166-implementers/topic/the.20concept.20of.20a.20clinical.20email