v0.21.0

• Changed (API): posts.send, and posts.create with send: true, now fail
  with a 403 system_domain_recipient_restricted (with restriction) when
  the team has no verified sending domain and the audience includes anyone
  outside the team, or the post sends from the built-in *.mailtea.email
  address. Nothing is sent or scheduled and the post stays a draft; on
  posts.create the error body carries the draft's id. The send used to be
  accepted and fail a moment later. A broadcast (kind: "broadcast") is never
  published to the website, however it is sent. No package change: this is
  the API's behaviour once it is deployed.

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Released from mailtea-app/mailtea@68b43c2.