Move configuration to traditional way

⭐️ This is the way.

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

docs/administration/configure/email.md

@@ -0,0 +1,31 @@
+# Email
+
+Mobilizon requires a SMTP server to deliver emails. Using 3rd-party mail providers (Mandrill, SendGrid, Mailjet, …) will be possible in the future.
+
+## SMTP configuration
+
+Mobilizon default settings assumes a SMTP server listens on `localhost`, port `25`. To specify a specific server and credentials, you can add the following section in your `prod.secret.exs` file and modify credentials to your needs.
+```elixir
+config :mobilizon, Mobilizon.Web.Email.Mailer,
+  adapter: Bamboo.SMTPAdapter,
+  server: "localhost",
+  hostname: "localhost",
+  port: 25,
+  username: nil,
+  password: nil,
+  # can be `:always` or `:never`
+  tls: :if_available,
+  allowed_tls_versions: [:tlsv1, :"tlsv1.1", :"tlsv1.2"],
+  # can be `true`
+  ssl: false,
+  retries: 1,
+  # can be `true`
+  no_mx_lookups: false,
+  # can be `:always`. If your smtp relay requires authentication set it to `:always`.
+  auth: :if_available
+```
+
+!!! tip
+    The hostname option sets the FQDN to the header of your emails, its optional, but if you don't set it, the underlying `gen_smtp` module will use the hostname of your machine, like `localhost`.
+
+You'll need to restart Mobilizon to recompile the app and apply the new settings.