diff --git a/app/models/domain_allow.rb b/app/models/domain_allow.rb
index 8eab3164e5b..783269bf258 100644
--- a/app/models/domain_allow.rb
+++ b/app/models/domain_allow.rb
@@ -33,7 +33,7 @@ class DomainAllow < ApplicationRecord
     def rule_for(domain)
       return if domain.blank?
 
-      uri = Addressable::URI.new.tap { |u| u.host = domain.delete('/') }
+      uri = Addressable::URI.new.tap { |u| u.host = domain.strip.delete('/') }
 
       find_by(domain: uri.normalized_host)
     end
diff --git a/spec/models/domain_allow_spec.rb b/spec/models/domain_allow_spec.rb
index 0c69aaff8dc..ac0c113d3a9 100644
--- a/spec/models/domain_allow_spec.rb
+++ b/spec/models/domain_allow_spec.rb
@@ -27,4 +27,27 @@ RSpec.describe DomainAllow do
       it { is_expected.to contain_exactly(allowed_domain.domain, other_allowed_domain.domain) }
     end
   end
+
+  describe '.rule_for' do
+    subject { described_class.rule_for(domain) }
+
+    let(:domain) { 'host.example' }
+
+    context 'with no records' do
+      it { is_expected.to be_nil }
+    end
+
+    context 'with matching record' do
+      let!(:domain_allow) { Fabricate :domain_allow, domain: }
+
+      it { is_expected.to eq(domain_allow) }
+    end
+
+    context 'when called with non normalized string' do
+      let!(:domain_allow) { Fabricate :domain_allow, domain: }
+      let(:domain) { '  HOST.example/' }
+
+      it { is_expected.to eq(domain_allow) }
+    end
+  end
 end
diff --git a/spec/models/domain_block_spec.rb b/spec/models/domain_block_spec.rb
index 14f904ea7fa..e7f463c8f56 100644
--- a/spec/models/domain_block_spec.rb
+++ b/spec/models/domain_block_spec.rb
@@ -35,6 +35,17 @@ RSpec.describe DomainBlock do
       expect(described_class.rule_for('example.com')).to eq block
     end
 
+    it 'returns most specific rule matching a blocked domain' do
+      _block = Fabricate(:domain_block, domain: 'example.com')
+      blog_block = Fabricate(:domain_block, domain: 'blog.example.com')
+      expect(described_class.rule_for('host.blog.example.com')).to eq blog_block
+    end
+
+    it 'returns rule matching a blocked domain when string needs normalization' do
+      block = Fabricate(:domain_block, domain: 'example.com')
+      expect(described_class.rule_for('  example.com/')).to eq block
+    end
+
     it 'returns a rule matching a subdomain of a blocked domain' do
       block = Fabricate(:domain_block, domain: 'example.com')
       expect(described_class.rule_for('sub.example.com')).to eq block
diff --git a/spec/models/email_domain_block_spec.rb b/spec/models/email_domain_block_spec.rb
index 5874c5e53c4..c3662b2d6cd 100644
--- a/spec/models/email_domain_block_spec.rb
+++ b/spec/models/email_domain_block_spec.rb
@@ -4,6 +4,8 @@ require 'rails_helper'
 
 RSpec.describe EmailDomainBlock do
   describe 'block?' do
+    subject { described_class.block?(input) }
+
     let(:input) { nil }
 
     context 'when given an e-mail address' do
@@ -14,12 +16,12 @@ RSpec.describe EmailDomainBlock do
 
         it 'returns true if the domain is blocked' do
           Fabricate(:email_domain_block, domain: 'example.com')
-          expect(described_class.block?(input)).to be true
+          expect(subject).to be true
         end
 
         it 'returns false if the domain is not blocked' do
           Fabricate(:email_domain_block, domain: 'other-example.com')
-          expect(described_class.block?(input)).to be false
+          expect(subject).to be false
         end
       end
 
@@ -28,7 +30,7 @@ RSpec.describe EmailDomainBlock do
 
         it 'returns true if it is a subdomain of a blocked domain' do
           Fabricate(:email_domain_block, domain: 'example.com')
-          expect(described_class.block?(input)).to be true
+          expect(subject).to be true
         end
       end
     end
@@ -38,8 +40,40 @@ RSpec.describe EmailDomainBlock do
 
       it 'returns true if the domain is blocked' do
         Fabricate(:email_domain_block, domain: 'mail.foo.com')
-        expect(described_class.block?(input)).to be true
+        expect(subject).to be true
       end
     end
+
+    context 'when given nil' do
+      it { is_expected.to be false }
+    end
+
+    context 'when given empty string' do
+      let(:input) { '' }
+
+      it { is_expected.to be true }
+    end
+  end
+
+  describe '.requires_approval?' do
+    subject { described_class.requires_approval?(input) }
+
+    let(:input) { nil }
+
+    context 'with a matching block requiring approval' do
+      before { Fabricate :email_domain_block, domain: input, allow_with_approval: true }
+
+      let(:input) { 'host.example' }
+
+      it { is_expected.to be true }
+    end
+
+    context 'with a matching block not requiring approval' do
+      before { Fabricate :email_domain_block, domain: input, allow_with_approval: false }
+
+      let(:input) { 'host.example' }
+
+      it { is_expected.to be false }
+    end
   end
 end
diff --git a/spec/models/preview_card_provider_spec.rb b/spec/models/preview_card_provider_spec.rb
index 561c93d0b25..cd3283faa3f 100644
--- a/spec/models/preview_card_provider_spec.rb
+++ b/spec/models/preview_card_provider_spec.rb
@@ -25,4 +25,36 @@ RSpec.describe PreviewCardProvider do
       end
     end
   end
+
+  describe '.matching_domain' do
+    subject { described_class.matching_domain(domain) }
+
+    let(:domain) { 'host.example' }
+
+    context 'without matching domains' do
+      it { is_expected.to be_nil }
+    end
+
+    context 'with exact matching domain' do
+      let!(:preview_card_provider) { Fabricate :preview_card_provider, domain: 'host.example' }
+
+      it { is_expected.to eq(preview_card_provider) }
+    end
+
+    context 'with matching domain segment' do
+      let!(:preview_card_provider) { Fabricate :preview_card_provider, domain: 'host.example' }
+      let(:domain) { 'www.blog.host.example' }
+
+      it { is_expected.to eq(preview_card_provider) }
+    end
+
+    context 'with multiple matching records' do
+      let!(:preview_card_provider_more) { Fabricate :preview_card_provider, domain: 'blog.host.example' }
+      let(:domain) { 'www.blog.host.example' }
+
+      before { Fabricate :preview_card_provider, domain: 'host.example' }
+
+      it { is_expected.to eq(preview_card_provider_more) }
+    end
+  end
 end