diff --git a/CHANGELOG.md b/CHANGELOG.md
index f8cec42..e6e31b8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Change log
 
+## 3.0.27 (2023-12-13)
+
+* Add format `mailbox` to `str` node for Schemacop3 schemas
+
 ## 3.0.26 (2023-11-16)
 
 * Lock dependency `ruby2_keywords` to the more open `>= 0.0.4`
diff --git a/README_V3.md b/README_V3.md
index f80a33d..449a7fd 100644
--- a/README_V3.md
+++ b/README_V3.md
@@ -243,6 +243,11 @@ transformed into various types.
   Validates for a valid email address. There is no casting involved since email
   addresses do not have their own ruby type.
 
+* `mailbox`
+  Validates for a valid mailbox, which is defined as a valid email enclosed in
+  brackets (`< >`), with an optional name before the email address. There is no
+  casting involved.
+
 * `boolean`
   The string must be either `true`, `false`, `0` or `1`. This value will be
   casted to Ruby's `TrueClass` or `FalseClass`. Please note that the strings
diff --git a/lib/schemacop.rb b/lib/schemacop.rb
index deba600..28d8b2d 100644
--- a/lib/schemacop.rb
+++ b/lib/schemacop.rb
@@ -55,6 +55,12 @@ def self.register_string_formatter(name, pattern:, handler:)
     handler: ->(value) { value }
   )
 
+  register_string_formatter(
+    :mailbox,
+    pattern: %r{^.*\s?<[a-zA-Z0-9.!\#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*>$},
+    handler: ->(value) { value }
+  )
+
   register_string_formatter(
     :boolean,
     pattern: /^(true|false|0|1)$/i,
diff --git a/test/unit/schemacop/v3/string_node_test.rb b/test/unit/schemacop/v3/string_node_test.rb
index 3edff10..43bac85 100644
--- a/test/unit/schemacop/v3/string_node_test.rb
+++ b/test/unit/schemacop/v3/string_node_test.rb
@@ -191,6 +191,50 @@ def test_format_email
         assert_cast('john.doe@example.com', 'john.doe@example.com')
       end
 
+      def test_format_mailbox
+        schema :string, format: :mailbox
+
+        assert_json(type: :string, format: :mailbox)
+
+        assert_validation 'john.doe@example.com' do
+          error '/', 'String does not match format "mailbox".'
+        end
+
+        assert_validation 'john.doe+foo-bar_baz@example.com' do
+          error '/', 'String does not match format "mailbox".'
+        end
+
+        assert_validation 'JOHN.DOE+FOO-BAR_BAZ@EXAMPLE.COM' do
+          error '/', 'String does not match format "mailbox".'
+        end
+
+        assert_validation 'someemail' do
+          error '/', 'String does not match format "mailbox".'
+        end
+
+        assert_validation 'john doe@example.com' do
+          error '/', 'String does not match format "mailbox".'
+        end
+
+        assert_validation '@john@example.com' do
+          error '/', 'String does not match format "mailbox".'
+        end
+
+        assert_validation 'John Doe <john.doe@example.com>'
+        assert_validation 'John Doe <john.doe+foo-bar_baz@example.com>'
+        assert_validation 'John Doe <JOHN.DOE+FOO-BAR_BAZ@EXAMPLE.COM>'
+
+        assert_validation 'John <john.doe@example.com>'
+        assert_validation 'John Doe 123 <john.doe@example.com>'
+        assert_validation 'John_Doe <john.doe@example.com>'
+        assert_validation 'John-Doe ÖÄ <john.doe@example.com>'
+        assert_validation '"John Doe" <john.doe@example.com>'
+        assert_validation '<john.doe@example.com>'
+
+        assert_cast(nil, nil)
+        assert_cast('John Doe <john.doe@example.com>', 'John Doe <john.doe@example.com>')
+      end
+
       def test_format_boolean
         schema :string, format: :boolean