diff --git a/README.md b/README.md
index c7625286c..58a1a9682 100644
--- a/README.md
+++ b/README.md
@@ -73,7 +73,7 @@ Beta is primarily intended for testing product features.
 
 Beta tenant is:
 
-- https://fizzy.37signals.works/
+- https://fizzy-beta.37signals.com
 
 This environment uses local disk for Active Storage.
 
diff --git a/config/environments/beta.rb b/config/environments/beta.rb
index c7f44040b..c67135679 100644
--- a/config/environments/beta.rb
+++ b/config/environments/beta.rb
@@ -1,7 +1,11 @@
 require_relative "production"
 
 Rails.application.configure do
-  config.action_mailer.default_url_options = { host: "%{tenant}.37signals.works" }
+  config.hosts = [ "fizzy-beta.37signals.com" ] + config.hosts[1..]
+
+  config.action_mailer.smtp_settings[:domain] = config.hosts.first
+  config.action_mailer.smtp_settings[:address] = "smtp-outbound-staging"
+  config.action_mailer.default_url_options = { host: config.hosts.first, protocol: "https" }
 
   # Let's keep beta on local disk. See https://github.com/basecamp/fizzy/pull/557 for context.
   config.active_storage.service = :local
diff --git a/config/environments/development.rb b/config/environments/development.rb
index 24fc6c04c..002ee99ed 100644
--- a/config/environments/development.rb
+++ b/config/environments/development.rb
@@ -75,6 +75,11 @@ Rails.application.configure do
   # Allow all hosts in development
   config.hosts = nil
 
+  config.hosts = %w[ fizzy.localhost localhost 127.0.0.1 ]
+
+  # Host to be used in links rendered from ActionMailer
+  config.action_mailer.default_url_options = { host: config.hosts.first, port: 3005 }
+
   if Rails.root.join("tmp/solid-queue.txt").exist?
     config.active_job.queue_adapter = :solid_queue
     config.solid_queue.connects_to = { database: { writing: :queue } }
diff --git a/config/environments/production.rb b/config/environments/production.rb
index 73f7f6f1b..664c60834 100644
--- a/config/environments/production.rb
+++ b/config/environments/production.rb
@@ -73,8 +73,17 @@ Rails.application.configure do
   # Set this to true and configure the email server for immediate delivery to raise delivery errors.
   # config.action_mailer.raise_delivery_errors = false
 
+  # Enable DNS rebinding protection and other `Host` header attacks.
+  config.hosts = [
+    "fizzy.37signals.com",
+    "localhost",
+    IPAddr.new("172.17.0.0/20") # Docker VPC
+  ]
+
   # Set host to be used by links generated in mailer templates.
-  config.action_mailer.default_url_options = { host: "%{tenant}.fizzy.37signals.com" }
+  config.action_mailer.default_url_options = { host: config.hosts.first, protocol: "https" }
+
+  config.action_mailer.smtp_settings = { domain: config.hosts.first, address: "smtp-outbound", port: 25, enable_starttls_auto: false }
 
   # Enable locale fallbacks for I18n (makes lookups for any locale fall back to
   # the I18n.default_locale when a translation cannot be found).
@@ -86,11 +95,6 @@ Rails.application.configure do
   # Do not dump schema after migrations.
   config.active_record.dump_schema_after_migration = false
 
-  # Enable DNS rebinding protection and other `Host` header attacks.
-  # config.hosts = [
-  #   "example.com",     # Allow requests from example.com
-  #   /.*\.example\.com/ # Allow requests from subdomains like `www.example.com`
-  # ]
   # Skip DNS rebinding protection for the default health check endpoint.
   # config.host_authorization = { exclude: ->(request) { request.path == "/up" } }
 end
diff --git a/config/environments/staging.rb b/config/environments/staging.rb
index 27868fd80..7bee9c845 100644
--- a/config/environments/staging.rb
+++ b/config/environments/staging.rb
@@ -1,5 +1,9 @@
 require_relative "production"
 
 Rails.application.configure do
-  config.action_mailer.default_url_options = { host: "%{tenant}.fizzy.37signals-staging.com" }
+  config.hosts = [ "fizzy.37signals-staging.com" ] + config.hosts[1..]
+
+  config.action_mailer.smtp_settings[:domain] = config.hosts.first
+  config.action_mailer.smtp_settings[:address] = "smtp-outbound-staging"
+  config.action_mailer.default_url_options = { host: config.hosts.first, protocol: "https" }
 end