diff --git a/CLAUDE.md b/CLAUDE.md
index 10cab81..efb5c79 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -38,7 +38,10 @@ The SDK has two independent subsystems sharing a common error hierarchy:
 Error
 ├── HttpRequestError (has status_code, response_body)
 │   ├── ValidationError (422, has error_type)
-│   └── ClientError (400)
+│   ├── ClientError (400)
+│   ├── AuthenticationError (401/403)
+│   └── RateLimitError (429, has retry_after)
+├── ConnectionError (has original_exception)
 ├── TimeoutError
 └── WebhookVerificationError
     ├── InvalidSignatureError
diff --git a/lib/lettermint/http_client.rb b/lib/lettermint/http_client.rb
index b148a2e..6863bb7 100644
--- a/lib/lettermint/http_client.rb
+++ b/lib/lettermint/http_client.rb
@@ -62,8 +62,12 @@ def with_error_handling
       handle_response(response)
     rescue Faraday::TimeoutError, Timeout::Error
       raise Lettermint::TimeoutError, "Request timeout after #{@connection.options.timeout}s"
+    rescue Faraday::SSLError => e
+      raise Lettermint::ConnectionError.new(message: "SSL error: #{e.message}", original_exception: e)
     rescue Faraday::ConnectionFailed => e
       raise Lettermint::ConnectionError.new(message: e.message, original_exception: e)
+    rescue Faraday::ParsingError => e
+      raise Lettermint::Error, "Failed to parse API response: #{e.message}"
     end
 
     def handle_response(response)
diff --git a/spec/lettermint/http_client_spec.rb b/spec/lettermint/http_client_spec.rb
index d887ba3..2b2f398 100644
--- a/spec/lettermint/http_client_spec.rb
+++ b/spec/lettermint/http_client_spec.rb
@@ -195,6 +195,38 @@
           expect(e.original_exception).to be_a(Faraday::ConnectionFailed)
         }
     end
+
+    it 'raises HttpRequestError on non-JSON error response body' do
+      stub_request(:post, "#{base_url}/send")
+        .to_return(
+          status: 500,
+          body: 'Internal Server Error',
+          headers: { 'Content-Type' => 'text/plain' }
+        )
+
+      expect { client.post(path: '/send', data: {}) }
+        .to raise_error(Lettermint::HttpRequestError) { |e|
+          expect(e.status_code).to eq(500)
+          expect(e.response_body).to be_nil
+          expect(e.message).to eq('HTTP 500')
+        }
+    end
+
+    it 'raises ConnectionError on SSL failure' do
+      stub_request(:post, "#{base_url}/send").to_raise(Faraday::SSLError.new('certificate verify failed'))
+
+      expect { client.post(path: '/send', data: {}) }
+        .to raise_error(Lettermint::ConnectionError, /SSL error:.*certificate verify failed/) { |e|
+          expect(e.original_exception).to be_a(Faraday::SSLError)
+        }
+    end
+
+    it 'raises Error on JSON parsing failure' do
+      stub_request(:post, "#{base_url}/send").to_raise(Faraday::ParsingError.new('unexpected token'))
+
+      expect { client.post(path: '/send', data: {}) }
+        .to raise_error(Lettermint::Error, /unexpected token|parsing/i)
+    end
   end
 
   describe 'custom base URL' do