diff --git a/app/controllers/registrations_controller.rb b/app/controllers/registrations_controller.rb
index f3d51b938..26942f5d1 100644
--- a/app/controllers/registrations_controller.rb
+++ b/app/controllers/registrations_controller.rb
@@ -64,10 +64,12 @@ class RegistrationsController < Devise::RegistrationsController
 
   def check_allowed_email(resource)
     domain = resource.email.split("@").last
-    allow_list = Settings::Authentication.allowed_registration_email_domains
-    return if allow_list.empty? || allow_list.include?(domain)
+    return true if Settings::Authentication.acceptable_domain?(domain: domain)
 
     resource.email = nil
+    # Alright, this error message isn't quite correct.  Is the email
+    # from a blocked domain?  Or an explicitly allowed domain.  I
+    # think this is enough.
     resource.errors.add(:email, "is not included in allowed domains.")
   end
 
diff --git a/app/lib/constants/settings/authentication.rb b/app/lib/constants/settings/authentication.rb
index fca778e43..1d14231b8 100644
--- a/app/lib/constants/settings/authentication.rb
+++ b/app/lib/constants/settings/authentication.rb
@@ -26,6 +26,10 @@ module Constants
           "The \"PEM\" key from the Authentication Service configured in the Apple Developer Portal",
           placeholder: "-----BEGIN PRIVATE KEY-----\nMIGTAQrux...QPe8Yb\n-----END PRIVATE KEY-----\\n"
         },
+        blocked_registration_email_domains: {
+          description: "Block registration from specified domains?  (comma-separated list)",
+          placeholder: "seo-hunt.com"
+        },
         display_email_domain_allow_list_publicly: {
           description: "Do you want to display the list of allowed domains, or keep it private?"
         },
diff --git a/app/models/settings/authentication.rb b/app/models/settings/authentication.rb
index e98f0afd3..8fff8121d 100644
--- a/app/models/settings/authentication.rb
+++ b/app/models/settings/authentication.rb
@@ -11,6 +11,9 @@ module Settings
     setting :apple_key_id, type: :string
     setting :apple_pem, type: :string
     setting :apple_team_id, type: :string
+    setting :blocked_registration_email_domains, type: :array, default: %(), validates: {
+      valid_domain_csv: true
+    }
     setting :display_email_domain_allow_list_publicly, type: :boolean, default: false
     setting :facebook_key, type: :string
     setting :facebook_secret, type: :string
@@ -38,5 +41,16 @@ module Settings
       "present"
     end
     singleton_class.alias_method(:apple_secret, :apple_key)
+
+    # @param domain [String] The domain to check for acceptability
+    #
+    # @return [Boolean] do we allow this domain?
+    def self.acceptable_domain?(domain:)
+      return false if blocked_registration_email_domains.include?(domain)
+      return true if allowed_registration_email_domains.empty?
+      return true if allowed_registration_email_domains.include?(domain)
+
+      false
+    end
   end
 end
diff --git a/app/views/admin/settings/forms/_authentication.html.erb b/app/views/admin/settings/forms/_authentication.html.erb
index 2dc85975f..66dcd0f08 100644
--- a/app/views/admin/settings/forms/_authentication.html.erb
+++ b/app/views/admin/settings/forms/_authentication.html.erb
@@ -95,6 +95,14 @@
                     <%= admin_config_description Constants::Settings::Authentication::DETAILS[:display_email_domain_allow_list_publicly][:description] %>
                   </div>
                 </div>
+                <div class="crayons-field">
+                  <%= admin_config_label :blocked_registration_email_domains, "Block email domains", model: Settings::Authentication %>
+                  <%= admin_config_description Constants::Settings::Authentication::DETAILS[:blocked_registration_email_domains][:description] %>
+                  <%= f.text_field :blocked_registration_email_domains,
+                                   class: "crayons-textfield",
+                                   value: Settings::Authentication.blocked_registration_email_domains.join(","),
+                                   placeholder: Constants::Settings::Authentication::DETAILS[:blocked_registration_email_domains][:placeholder] %>
+                </div>
                 <div class="crayons-field--checkbox">
                   <%= f.check_box :require_captcha_for_email_password_registration,
                                   checked: Settings::Authentication.require_captcha_for_email_password_registration,
diff --git a/spec/models/settings/authentication_spec.rb b/spec/models/settings/authentication_spec.rb
index ca7b686f8..af062c21f 100644
--- a/spec/models/settings/authentication_spec.rb
+++ b/spec/models/settings/authentication_spec.rb
@@ -1,8 +1,60 @@
 require "rails_helper"
 
 RSpec.describe Settings::Authentication, type: :model do
+  describe "#acceptable_domain?" do
+    subject { described_class.acceptable_domain?(domain: domain) }
+
+    let(:domain) { "hello.com" }
+
+    context "with blocked domain" do
+      before do
+        allow(described_class).to receive(:blocked_registration_email_domains).and_return([domain])
+      end
+
+      it { is_expected.to be_falsey }
+    end
+
+    context "with allowed domain" do
+      before do
+        allow(described_class).to receive(:allowed_registration_email_domains).and_return([domain])
+      end
+
+      it { is_expected.to be_truthy }
+    end
+
+    context "with no domains blocked nor explicitly allowed" do
+      before do
+        allow(described_class).to receive(:allowed_registration_email_domains).and_return([])
+      end
+
+      it { is_expected.to be_truthy }
+    end
+
+    context "with no domains blocked but an explicitly allowed domain" do
+      before do
+        allow(described_class).to receive(:allowed_registration_email_domains).and_return(["wonka.vision"])
+      end
+
+      it { is_expected.to be_falsey }
+    end
+  end
+
   describe "validations" do
-    describe "validating domain lists" do
+    describe "#blocked_registration_email_domains" do
+      it "allows valid domain lists" do
+        expect do
+          described_class.blocked_registration_email_domains = "example.com, example2.com"
+        end.not_to raise_error
+      end
+
+      it "rejects invalid domain lists" do
+        expect do
+          described_class.blocked_registration_email_domains = "example.com, e.c"
+        end.to raise_error(/must be a comma-separated list of valid domains/)
+      end
+    end
+
+    describe "#allowed_registration_email_domains" do
       it "allows valid domain lists" do
         expect do
           described_class.allowed_registration_email_domains = "example.com, example2.com"