Add custom mailer for one-off emails

app/mailers/application_mailer.rb

@@ -1,4 +1,3 @@
 class ApplicationMailer < ActionMailer::Base
-  default from: 'from@example.com'
   layout 'mailer'
 end

app/mailers/custom_mailer.rb

@@ -0,0 +1,23 @@
+# A custom mailer that can be used from the Rails console for one-off emails
+# today, and later connected from an admin panel mailing page.
+#
+# Assign any template variables you want to use:
+#
+#     user = User.first
+#
+# Create the email body from a custom email template file:
+#
+#     body = ERB.new(File.read('./tmp/mailer-1.txt.erb')).result binding
+#
+# Send email via Sidekiq:
+#
+#     CustomMailer.with(user: u, subject: "Important announcement", body: body).custom_message.deliver_later
+#
+class CustomMailer < ApplicationMailer
+  def custom_message
+    @user = params[:user]
+    @subject = params[:subject]
+    @body = params[:body]
+    mail(to: @user.email, subject: @subject)
+  end
+end