Function MyWeb.Bamboo.SentEmailViewerPlug.init/1 is undefined

Take a look here if you haven’t Bamboo.LocalAdapter — bamboo v2.5.0

This part

Example config

# In config/config.exs, or config/dev.exs, etc.
config :my_app, MyApp.Mailer,
  adapter: Bamboo.LocalAdapter,
  open_email_in_browser_url: "http://localhost:4000/sent_emails" # optional

# Define a Mailer. Maybe in lib/my_app/mailer.ex
defmodule MyApp.Mailer do
  use Bamboo.Mailer, otp_app: :my_app
end