[README] Copy over documentation

CONTRIBUTING.md

@@ -64,6 +64,10 @@ All tests should pass when running:
 
 `bundle exec rspec`
 
+### Updating AWS Fixtures for SES Action Mailbox Ingestion
+
+`bundle exec rake sign_aws_fixtures`
+
 ## Finding contributions to work on
 
 Looking at the existing issues is a great way to find something to contribute

README.md

@@ -164,6 +164,93 @@ You simply need to configure Rails to use it in your environment configuration:
 config.action_mailer.delivery_method = :ses # or :sesv2
 ```
 
+## Amazon Simple Email Service (SES) as an ActionMailbox Method
+
+### Configuration
+
+#### Amazon SES/SNS
+
+1. [Configure SES](https://docs.aws.amazon.com/ses/latest/DeveloperGuide/receiving-email-notifications.html) to (save emails to S3)(https://docs.aws.amazon.com/ses/latest/dg/receiving-email-action-s3.html) or to send them as raw messages.
+
+2. [Configure the SNS topic for SES or for the S3 action](https://docs.aws.amazon.com/ses/latest/DeveloperGuide/receiving-email-action-sns.html) to send notifications to +/rails/action_mailbox/amazon/inbound_emails+. For example, if your website is hosted at https://www.example.com then configure _SNS_ to publish the _SES_ notification topic to this _HTTP_ endpoint: https://example.com/rails/action_mailbox/amazon/inbound_emails
+
+#### Rails
+
+1. Configure _ActionMailbox_ to accept emails from Amazon SES:
+
+```
+# config/environments/production.rb
+config.action_mailbox.ingress = :amazon
+```
+
+2. Configure which _SNS_ topics will be accepted:
+
+```
+# config/environments/production.rb
+config.action_mailbox.amazon.subscribed_topics = %w(
+  arn:aws:sns:eu-west-1:123456789001:example-topic-1
+  arn:aws:sns:us-east-1:123456789002:example-topic-2
+)
+```
+
+SNS Subscriptions will now be auto-confirmed and messages will be automatically handled via _ActionMailbox_.
+
+Note that even if you manually confirm subscriptions you will still need to provide a list of subscribed topics; messages from unrecognized topics will be ignored.
+
+See [ActionMailbox documentation](https://guides.rubyonrails.org/action_mailbox_basics.html) for full usage information.
+
+### Testing
+
+#### RSpec
+
+Two _RSpec_ _request spec_ helpers are provided to facilitate testing _Amazon SNS/SES_ notifications in your application:
+
+* `amazon_ingress_deliver_subscription_confirmation`
+* `amazon_ingress_deliver_email`
+
+Include the `ActionMailboxAmazonIngress::RSpec` extension in your tests:
+
+```ruby
+# spec/rails_helper.rb
+
+require 'aws/rails/action_mailbox/rspec'
+
+RSpec.configure do |config|
+  config.include Aws::Rails::ActionMailbox::RSpec
+end
+```
+
+Configure your _test_ environment to accept the default topic used by the provided helpers:
+
+```ruby
+# config/environments/test.rb
+
+config.action_mailbox.amazon.subscribed_topics = ['topic:arn:default']
+```
+
+##### Example Usage
+
+```ruby
+# spec/requests/amazon_emails_spec.rb
+
+RSpec.describe 'amazon emails', type: :request do
+  it 'delivers a subscription notification' do
+    amazon_ingress_deliver_subscription_confirmation
+    expect(response).to have_http_status :ok
+  end
+
+  it 'delivers an email notification' do
+    amazon_ingress_deliver_email(mail: Mail.new(to: 'user@example.com'))
+    expect(ActionMailbox::InboundEmail.last.mail.recipients).to eql ['user@example.com']
+  end
+end
+```
+
+You may also pass the following keyword arguments to both helpers:
+
+* `topic`: The _SNS_ topic used for each notification (default: `topic:arn:default`).
+* `authentic`: The `Aws::SNS::MessageVerifier` class is stubbed by these helpers; set `authentic` to `true` or `false` to define how it will verify incoming notifications (default: `true`).
+
 ### Override credentials or other client options
 
 Client options can be overridden by re-registering the mailer with any set of