Sends email using Postmarks's API.

Use this adapter to send emails through Postmark's API. Requires that an API key is set in the config.

Example config

# In config/config.exs, or config.prod.exs, etc.
config :my_app, MyApp.Mailer,
  adapter: Bamboo.PostmarkAdapter,
  api_key: "my_api_key" or {:system, "POSTMARK_API_KEY"}