diff --git a/src/main/java/fr/ippon/example/intellijfeatures/controller/EmailController.java b/src/main/java/fr/ippon/example/intellijfeatures/controller/EmailController.java
index e590013..8f37101 100644
--- a/src/main/java/fr/ippon/example/intellijfeatures/controller/EmailController.java
+++ b/src/main/java/fr/ippon/example/intellijfeatures/controller/EmailController.java
@@ -2,6 +2,7 @@ package fr.ippon.example.intellijfeatures.controller;
 
 import fr.ippon.example.intellijfeatures.model.User;
 import fr.ippon.example.intellijfeatures.services.mail.EmailService;
+import fr.ippon.example.intellijfeatures.services.validator.UserValidator;
 import org.springframework.web.bind.annotation.*;
 
 import static org.springframework.http.HttpStatus.NO_CONTENT;
@@ -10,14 +11,17 @@ import static org.springframework.http.HttpStatus.NO_CONTENT;
 @RequestMapping("/api/mails")
 public class EmailController {
     private final EmailService emailService;
+    private final UserValidator userValidator;
 
-    public EmailController(EmailService emailService) {
+    public EmailController(EmailService emailService, UserValidator userValidator) {
         this.emailService = emailService;
+        this.userValidator = userValidator;
     }
 
     @PostMapping("/send")
     @ResponseStatus(NO_CONTENT)
     public void sendMail(@RequestBody User user) {
+        userValidator.check(user);
         emailService.sendMail(user);
     }
 }
diff --git a/src/main/java/fr/ippon/example/intellijfeatures/exception/BadRequestException.java b/src/main/java/fr/ippon/example/intellijfeatures/exception/BadRequestException.java
new file mode 100644
index 0000000..3f16f90
--- /dev/null
+++ b/src/main/java/fr/ippon/example/intellijfeatures/exception/BadRequestException.java
@@ -0,0 +1,15 @@
+package fr.ippon.example.intellijfeatures.exception;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.web.bind.annotation.ResponseStatus;
+
+@ResponseStatus(value = HttpStatus.BAD_REQUEST)
+public class BadRequestException extends BusinessException {
+    public BadRequestException(String message) {
+        super(message);
+    }
+
+    public BadRequestException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}
diff --git a/src/main/java/fr/ippon/example/intellijfeatures/exception/BusinessException.java b/src/main/java/fr/ippon/example/intellijfeatures/exception/BusinessException.java
new file mode 100644
index 0000000..1c0a23b
--- /dev/null
+++ b/src/main/java/fr/ippon/example/intellijfeatures/exception/BusinessException.java
@@ -0,0 +1,26 @@
+package fr.ippon.example.intellijfeatures.exception;
+
+/**
+ * Business exception.
+ */
+public class BusinessException extends RuntimeException {
+
+    public BusinessException() {}
+
+    /**
+     * Constructs an exception with a message.
+     * @param message The description of the error met.
+     */
+    public BusinessException(final String message) {
+        super(message);
+    }
+
+    /**
+     * Constructs an exception with a message and a code.
+     * @param message The description of the error met.
+     * @param cause The cause of the exception.
+     */
+    public BusinessException(final String message, final Throwable cause) {
+        super(message, cause);
+    }
+}
diff --git a/src/main/java/fr/ippon/example/intellijfeatures/services/validator/UserValidator.java b/src/main/java/fr/ippon/example/intellijfeatures/services/validator/UserValidator.java
new file mode 100644
index 0000000..8d405c5
--- /dev/null
+++ b/src/main/java/fr/ippon/example/intellijfeatures/services/validator/UserValidator.java
@@ -0,0 +1,21 @@
+package fr.ippon.example.intellijfeatures.services.validator;
+
+import fr.ippon.example.intellijfeatures.exception.BadRequestException;
+import fr.ippon.example.intellijfeatures.model.User;
+import org.springframework.stereotype.Component;
+import org.springframework.util.ObjectUtils;
+
+import java.util.regex.Pattern;
+
+@Component
+public class UserValidator {
+    public void check(User user) {
+        if (user.getName() == null || ObjectUtils.isEmpty(user.getName())) {
+            throw new BadRequestException("User name is required.");
+        }
+
+        if (user.getEmail() == null || !Pattern.matches("\\w+@\\w+\\.\\w+", user.getEmail())) {
+            throw new BadRequestException("User email is required and should be a valid email.");
+        }
+    }
+}
diff --git a/src/main/java/fr/ippon/example/intellijfeatures/torefactor/MonolithController.java b/src/main/java/fr/ippon/example/intellijfeatures/torefactor/MonolithController.java
new file mode 100644
index 0000000..4708e05
--- /dev/null
+++ b/src/main/java/fr/ippon/example/intellijfeatures/torefactor/MonolithController.java
@@ -0,0 +1,61 @@
+package fr.ippon.example.intellijfeatures.torefactor;
+
+import com.mitchellbosecke.pebble.PebbleEngine;
+import fr.ippon.example.intellijfeatures.exception.BadRequestException;
+import fr.ippon.example.intellijfeatures.model.User;
+import org.springframework.http.HttpStatus;
+import org.springframework.mail.javamail.JavaMailSender;
+import org.springframework.mail.javamail.MimeMessageHelper;
+import org.springframework.util.ObjectUtils;
+import org.springframework.util.StringUtils;
+import org.springframework.web.bind.annotation.*;
+
+import javax.mail.MessagingException;
+import javax.mail.internet.MimeMessage;
+import java.io.IOException;
+import java.io.StringWriter;
+import java.io.Writer;
+import java.util.Map;
+import java.util.regex.Pattern;
+
+@RestController
+@RequestMapping("/api/mail2")
+public class MonolithController {
+    private final JavaMailSender javaMailSender;
+
+    public MonolithController(JavaMailSender javaMailSender) {
+        this.javaMailSender = javaMailSender;
+    }
+
+    @PostMapping("/send")
+    @ResponseStatus(HttpStatus.NO_CONTENT)
+    public void sendMail(@RequestBody User user) throws IOException, MessagingException {
+        if (user.getName() == null || ObjectUtils.isEmpty(user.getName())) {
+            throw new BadRequestException("User name is required.");
+        }
+
+        if (user.getEmail() == null || !Pattern.matches("\\w+@\\w+\\.\\w+", user.getEmail())) {
+            throw new BadRequestException("User email is required and should be a valid email.");
+        }
+
+        PebbleEngine pebbleEngine = new PebbleEngine.Builder().build();
+
+        Writer writer = new StringWriter();
+        pebbleEngine.getTemplate("templates/mail/user-mail.html")
+                .evaluate(writer, Map.of("user", user));
+        String htmlContent = writer.toString();
+
+        Writer writer2 = new StringWriter();
+        pebbleEngine.getTemplate("templates/mail/user-mail.txt")
+                .evaluate(writer2, Map.of("user", user));
+        String textContent = writer2.toString();
+
+        MimeMessage mimeMessage = javaMailSender.createMimeMessage();
+
+        MimeMessageHelper helper = new MimeMessageHelper(mimeMessage, true);
+        helper.setTo(user.getEmail());
+        helper.setSubject("Hello");
+        helper.setText(textContent, htmlContent);
+        javaMailSender.send(mimeMessage);
+    }
+}
diff --git a/src/main/resources/application.yml b/src/main/resources/application.yml
index c496fff..8c1e807 100644
--- a/src/main/resources/application.yml
+++ b/src/main/resources/application.yml
@@ -1,3 +1,9 @@
+server:
+  error:
+    whitelabel:
+      enabled: false # Disable html error responses.
+    include-stacktrace: never
+
 spring:
   mail:
     host: localhost