diff --git a/spec/models/user_spec.rb b/spec/models/user_spec.rb
index 03d5388b7..9bc4cd07b 100644
--- a/spec/models/user_spec.rb
+++ b/spec/models/user_spec.rb
@@ -436,6 +436,29 @@ RSpec.describe User, type: :model do
         end
       end
     end
+
+    describe '#preferences' do
+      describe '"mail_delivery_failed{,_data}" keys' do
+        before do
+          user.update(
+            preferences: {
+              mail_delivery_failed:      true,
+              mail_delivery_failed_data: Time.current
+            }
+          )
+        end
+
+        it 'deletes "mail_delivery_failed"' do
+          expect { user.update(email: Faker::Internet.email) }
+            .to change { user.preferences.key?(:mail_delivery_failed) }.to(false)
+        end
+
+        it 'leaves "mail_delivery_failed_data" untouched' do
+          expect { user.update(email: Faker::Internet.email) }
+            .to not_change { user.preferences[:mail_delivery_failed_data] }
+        end
+      end
+    end
   end
 
   describe 'Associations:' do
diff --git a/test/unit/user_mail_delivery_failed_test.rb b/test/unit/user_mail_delivery_failed_test.rb
deleted file mode 100644
index 749e6e2fd..000000000
--- a/test/unit/user_mail_delivery_failed_test.rb
+++ /dev/null
@@ -1,40 +0,0 @@
-require 'test_helper'
-
-class UserMailDeliveryFailedTest < ActiveSupport::TestCase
-  setup do
-
-    UserInfo.current_user_id = 1
-
-    roles = Role.where(name: 'Customer')
-    @customer1 = User.create_or_update(
-      login:     'user-mail-delivery-failed-customer1@example.com',
-      firstname: 'UserOutOfOffice',
-      lastname:  'Customer1',
-      email:     'user-mail-delivery-failed-customer1@example.com',
-      password:  'agentpw',
-      active:    true,
-      roles:     roles,
-    )
-
-  end
-
-  test 'check reset of mail_delivery_failed' do
-
-    @customer1.preferences[:mail_delivery_failed] = true
-    @customer1.preferences[:mail_delivery_failed_data] = Time.zone.now
-    @customer1.save!
-    @customer1.reload
-
-    assert_equal(@customer1.preferences[:mail_delivery_failed], true)
-    assert(@customer1.preferences[:mail_delivery_failed_data])
-
-    @customer1.email = 'new-user-mail-delivery-failed-customer1@example.com'
-    @customer1.save!
-    @customer1.reload
-
-    assert_not(@customer1.preferences[:mail_delivery_failed], true)
-    assert(@customer1.preferences[:mail_delivery_failed_data])
-
-  end
-
-end