Add the configuration for the email.

config/runtime.exs

@@ -1,5 +1,6 @@
 import Config
 
+require Logger
 # config/runtime.exs is executed for all environments, including
 # during releases. It is executed after compilation and before the
 # system starts, so it is typically used to load production configuration
@@ -119,4 +120,33 @@ if config_env() == :prod do
   #     config :swoosh, :api_client, Swoosh.ApiClient.Hackney
   #
   # See https://hexdocs.pm/swoosh/Swoosh.html#module-installation for details.
+
+  if System.get_env("SMTP_EMAIL_RELAY") do
+    Logger.info("Using SMTP for email delivery")
+
+    config :decentralised_book_index, DecentralisedBookIndex.Mailer,
+      adapter: Swoosh.Adapters.SMTP,
+      relay: System.get_env("SMTP_EMAIL_RELAY"),
+      username: System.get_env("SMTP_EMAIL_USERNAME"),
+      password: System.get_env("SMTP_EMAIL_PASSWORD"),
+      ssl: true,
+      tls: :always,
+      auth: :always,
+      port: System.get_env("SMTP_EMAIL_PORT"),
+      retries: 2,
+      no_mx_lookups: false
+
+    config :swoosh, :api_client, Swoosh.ApiClient.Finch
+  end
+
+  if System.get_env("SCALEWAY_EMAIL_PROJECT_ID") do
+    Logger.info("Using Scaleway for email delivery")
+
+    config :decentralised_book_index, DecentralisedBookIndex.Mailer,
+      adapter: Swoosh.Adapters.Scaleway,
+      project_id: System.get_env("SCALEWAY_EMAIL_PROJECT_ID"),
+      secret_key: System.get_env("SCALEWAY_EMAIL_SECRET_KEY")
+
+    config :swoosh, :api_client, Swoosh.ApiClient.Finch
+  end
 end