namespace email settings keys per adapter

Settings keys like api_key were shared across providers, so switching
from e.g. Postmark to SendGrid showed the old API key. Now each
adapter gets its own namespaced key (email_postmark_api_key, etc.)
so credentials persist independently and switching back pre-fills
previously saved values.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/berrypod/mailer.ex

@@ -40,10 +40,12 @@ defmodule Berrypod.Mailer do
       adapter_info ->
         config =
           for field <- adapter_info.fields, into: %{} do
+            settings_key = Adapters.settings_key(adapter_info.key, field.key)
+
             value =
               case field.type do
-                :secret -> Settings.secret_hint("email_#{field.key}")
-                _ -> Settings.get_setting("email_#{field.key}")
+                :secret -> Settings.secret_hint(settings_key)
+                _ -> Settings.get_setting(settings_key)
               end
 
             {field.key, value}
@@ -114,7 +116,7 @@ defmodule Berrypod.Mailer do
     opts =
       for field <- adapter_info.fields, reduce: [] do
         acc ->
-          settings_key = "email_#{field.key}"
+          settings_key = Adapters.settings_key(adapter_info.key, field.key)
 
           value =
             case field.type do

lib/berrypod/mailer/adapters.ex

@@ -59,6 +59,17 @@ defmodule Berrypod.Mailer.Adapters do
         %Field{key: "secret", label: "Secret key", type: :secret, required: true}
       ]
     },
+    %Adapter{
+      key: "mailersend",
+      name: "MailerSend",
+      module: Swoosh.Adapters.MailerSend,
+      description: "Generous free tier, good analytics dashboard.",
+      tags: ["All email", "EU option"],
+      url: "https://www.mailersend.com",
+      fields: [
+        %Field{key: "api_key", label: "API key", type: :secret, required: true}
+      ]
+    },
     %Adapter{
       key: "resend",
       name: "Resend",
@@ -126,15 +137,18 @@ defmodule Berrypod.Mailer.Adapters do
     Enum.find(@adapters, &(&1.key == key))
   end
 
-  @doc "Returns the settings keys for an adapter's fields (prefixed with `email_`)."
-  def field_keys(%{fields: fields}) do
-    Enum.map(fields, &"email_#{&1.key}")
+  @doc "Returns the namespaced settings key for an adapter field."
+  def settings_key(adapter_key, field_key) do
+    "email_#{adapter_key}_#{field_key}"
+  end
+
+  @doc "Returns the settings keys for an adapter's fields."
+  def field_keys(%{key: adapter_key, fields: fields}) do
+    Enum.map(fields, &settings_key(adapter_key, &1.key))
   end
 
   @doc "Returns all possible settings keys across all adapters."
   def all_field_keys do
-    @adapters
-    |> Enum.flat_map(&field_keys/1)
-    |> Enum.uniq()
+    Enum.flat_map(@adapters, &field_keys/1)
   end
 end

lib/berrypod_web/live/admin/email_settings.ex

@@ -30,6 +30,26 @@ defmodule BerrypodWeb.Admin.EmailSettings do
      |> assign(:form, to_form(%{}, as: :email))}
   end
 
+  defp load_adapter_values(adapter_key) do
+    case Adapters.get(adapter_key) do
+      nil ->
+        %{}
+
+      adapter_info ->
+        for field <- adapter_info.fields, into: %{} do
+          settings_key = Adapters.settings_key(adapter_key, field.key)
+
+          value =
+            case field.type do
+              :secret -> Settings.secret_hint(settings_key)
+              _ -> Settings.get_setting(settings_key)
+            end
+
+          {field.key, value}
+        end
+    end
+  end
+
   defp provider_options do
     Enum.map(Adapters.all(), fn adapter ->
       %{
@@ -44,7 +64,8 @@ defmodule BerrypodWeb.Admin.EmailSettings do
 
   @impl true
   def handle_event("change_adapter", %{"email" => %{"adapter" => key}}, socket) do
-    {:noreply, assign(socket, :adapter_key, key)}
+    values = load_adapter_values(key)
+    {:noreply, socket |> assign(:adapter_key, key) |> assign(:current_values, values)}
   end
 
   def handle_event("save", %{"email" => params}, socket) do
@@ -113,8 +134,9 @@ defmodule BerrypodWeb.Admin.EmailSettings do
       |> Enum.filter(fn field ->
         val = params[field.key]
         empty = is_nil(val) or val == ""
+        settings_key = Adapters.settings_key(adapter_info.key, field.key)
         # Secret fields can be left blank to keep existing value
-        empty and not (field.type == :secret and Settings.get_secret("email_#{field.key}") != nil)
+        empty and not (field.type == :secret and Settings.get_secret(settings_key) != nil)
       end)
 
     if missing != [] do
@@ -124,17 +146,10 @@ defmodule BerrypodWeb.Admin.EmailSettings do
       # Save adapter type
       Settings.put_setting("email_adapter", adapter_info.key)
 
-      # Clear fields from other adapters
-      current_keys = MapSet.new(Enum.map(adapter_info.fields, &"email_#{&1.key}"))
-
-      for key <- Adapters.all_field_keys(), key not in current_keys do
-        Settings.delete_setting(key)
-      end
-
       # Save current adapter fields (blank secrets keep existing value)
       for field <- adapter_info.fields do
         value = params[field.key]
-        settings_key = "email_#{field.key}"
+        settings_key = Adapters.settings_key(adapter_info.key, field.key)
 
         cond do
           value && value != "" ->