Reviewable (https://reviewable.io https://reviewable.io) is built around this workflow: it will keep your drafts, let you review them, then send them all at onc

Reviewable (https://reviewable.io https://reviewable.io) is built around this workflow: it will keep your drafts, let you review them, then send them all at once (triggering a single notification email). Disclosure: I built the tool. :)