diff --git a/backend/build.gradle b/backend/build.gradle
index dd7ff6c..101e918 100644
--- a/backend/build.gradle
+++ b/backend/build.gradle
@@ -30,10 +30,12 @@ dependencies {
     implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
     implementation 'org.springframework.boot:spring-boot-starter-validation'
     implementation 'org.springframework.boot:spring-boot-starter-webmvc'
+    implementation 'org.mapstruct:mapstruct:1.6.3'
     compileOnly 'org.projectlombok:lombok'
     developmentOnly 'org.springframework.boot:spring-boot-devtools'
     runtimeOnly 'com.h2database:h2'
     annotationProcessor 'org.projectlombok:lombok'
+    annotationProcessor 'org.mapstruct:mapstruct-processor:1.6.3'
     testImplementation 'org.springframework.boot:spring-boot-starter-data-jdbc-test'
     testImplementation 'org.springframework.boot:spring-boot-starter-data-jpa-test'
     testImplementation 'org.springframework.boot:spring-boot-starter-validation-test'
diff --git a/backend/postman_collection.json b/backend/postman_collection.json
new file mode 100644
index 0000000..a67c35b
--- /dev/null
+++ b/backend/postman_collection.json
@@ -0,0 +1,232 @@
+{
+  "info": {
+    "name": "Users API - Server Manager",
+    "description": "Collection de testes para a API de Usuários",
+    "schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json"
+  },
+  "item": [
+    {
+      "name": "Users",
+      "item": [
+        {
+          "name": "Create User",
+          "request": {
+            "method": "POST",
+            "header": [
+              {
+                "key": "Content-Type",
+                "value": "application/json"
+              }
+            ],
+            "body": {
+              "mode": "raw",
+              "raw": "{\n  \"firstName\": \"João\",\n  \"lastName\": \"Silva\",\n  \"email\": \"joao.silva@hittelco.com\",\n  \"password\": \"senha123\"\n}"
+            },
+            "url": {
+              "raw": "{{base_url}}/api/users",
+              "host": [
+                "{{base_url}}"
+              ],
+              "path": [
+                "api",
+                "users"
+              ]
+            }
+          },
+          "response": []
+        },
+        {
+          "name": "Create User - Test 2",
+          "request": {
+            "method": "POST",
+            "header": [
+              {
+                "key": "Content-Type",
+                "value": "application/json"
+              }
+            ],
+            "body": {
+              "mode": "raw",
+              "raw": "{\n  \"firstName\": \"Maria\",\n  \"lastName\": \"Santos\",\n  \"email\": \"maria.santos@accesscommunications.com\",\n  \"password\": \"senha456\"\n}"
+            },
+            "url": {
+              "raw": "{{base_url}}/api/users",
+              "host": [
+                "{{base_url}}"
+              ],
+              "path": [
+                "api",
+                "users"
+              ]
+            }
+          },
+          "response": []
+        },
+        {
+          "name": "Create User - Invalid Domain",
+          "request": {
+            "method": "POST",
+            "header": [
+              {
+                "key": "Content-Type",
+                "value": "application/json"
+              }
+            ],
+            "body": {
+              "mode": "raw",
+              "raw": "{\n  \"firstName\": \"Carlos\",\n  \"lastName\": \"Oliveira\",\n  \"email\": \"carlos@gmail.com\",\n  \"password\": \"senha789\"\n}"
+            },
+            "url": {
+              "raw": "{{base_url}}/api/users",
+              "host": [
+                "{{base_url}}"
+              ],
+              "path": [
+                "api",
+                "users"
+              ]
+            }
+          },
+          "response": []
+        },
+        {
+          "name": "Get All Users",
+          "request": {
+            "method": "GET",
+            "header": [],
+            "url": {
+              "raw": "{{base_url}}/api/users",
+              "host": [
+                "{{base_url}}"
+              ],
+              "path": [
+                "api",
+                "users"
+              ]
+            }
+          },
+          "response": []
+        },
+        {
+          "name": "Get User by ID",
+          "request": {
+            "method": "GET",
+            "header": [],
+            "url": {
+              "raw": "{{base_url}}/api/users/{{user_id}}",
+              "host": [
+                "{{base_url}}"
+              ],
+              "path": [
+                "api",
+                "users",
+                "{{user_id}}"
+              ]
+            }
+          },
+          "response": []
+        },
+        {
+          "name": "Get User by Username",
+          "request": {
+            "method": "GET",
+            "header": [],
+            "url": {
+              "raw": "{{base_url}}/api/users/username/joao.silva@hittelco.com",
+              "host": [
+                "{{base_url}}"
+              ],
+              "path": [
+                "api",
+                "users",
+                "username",
+                "joao.silva@hittelco.com"
+              ]
+            }
+          },
+          "response": []
+        },
+        {
+          "name": "Get User by Email",
+          "request": {
+            "method": "GET",
+            "header": [],
+            "url": {
+              "raw": "{{base_url}}/api/users/email/maria.santos@accesscommunications.com",
+              "host": [
+                "{{base_url}}"
+              ],
+              "path": [
+                "api",
+                "users",
+                "email",
+                "maria.santos@accesscommunications.com"
+              ]
+            }
+          },
+          "response": []
+        },
+        {
+          "name": "Update User",
+          "request": {
+            "method": "PUT",
+            "header": [
+              {
+                "key": "Content-Type",
+                "value": "application/json"
+              }
+            ],
+            "body": {
+              "mode": "raw",
+              "raw": "{\n  \"firstName\": \"João Paulo\",\n  \"lastName\": \"Silva Santos\",\n  \"email\": \"joao.paulo@hittelco.com\",\n  \"password\": \"novaSenha123\"\n}"
+            },
+            "url": {
+              "raw": "{{base_url}}/api/users/{{user_id}}",
+              "host": [
+                "{{base_url}}"
+              ],
+              "path": [
+                "api",
+                "users",
+                "{{user_id}}"
+              ]
+            }
+          },
+          "response": []
+        },
+        {
+          "name": "Delete User",
+          "request": {
+            "method": "DELETE",
+            "header": [],
+            "url": {
+              "raw": "{{base_url}}/api/users/{{user_id}}",
+              "host": [
+                "{{base_url}}"
+              ],
+              "path": [
+                "api",
+                "users",
+                "{{user_id}}"
+              ]
+            }
+          },
+          "response": []
+        }
+      ]
+    }
+  ],
+  "variable": [
+    {
+      "key": "base_url",
+      "value": "http://localhost:8080",
+      "type": "string"
+    },
+    {
+      "key": "user_id",
+      "value": "",
+      "type": "string"
+    }
+  ]
+}
+
diff --git a/backend/src/main/java/com/hitcommunications/servermanager/BackendApplication.java b/backend/src/main/java/com/hitcommunications/servermanager/BackendApplication.java
index aacf78c..499432d 100644
--- a/backend/src/main/java/com/hitcommunications/servermanager/BackendApplication.java
+++ b/backend/src/main/java/com/hitcommunications/servermanager/BackendApplication.java
@@ -17,4 +17,4 @@ public class BackendApplication {
     public String home() {
         return "Hello, World!";
     }
-}
+}
\ No newline at end of file
diff --git a/backend/src/main/java/com/hitcommunications/servermanager/controllers/UsersController.java b/backend/src/main/java/com/hitcommunications/servermanager/controllers/UsersController.java
new file mode 100644
index 0000000..6f22abb
--- /dev/null
+++ b/backend/src/main/java/com/hitcommunications/servermanager/controllers/UsersController.java
@@ -0,0 +1,56 @@
+package com.hitcommunications.servermanager.controllers;
+
+import com.hitcommunications.servermanager.model.dtos.NewUserDTO;
+import com.hitcommunications.servermanager.model.dtos.UserDTO;
+import com.hitcommunications.servermanager.services.UsersService;
+import jakarta.validation.Valid;
+import lombok.RequiredArgsConstructor;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.*;
+
+import java.util.List;
+import java.util.UUID;
+
+@RestController
+@RequestMapping("/api/users")
+@RequiredArgsConstructor
+public class UsersController {
+
+    private final UsersService usersService;
+
+    @PostMapping
+    public ResponseEntity<UserDTO> create(@RequestBody @Valid NewUserDTO crateDTO) throws IllegalAccessException {
+       return ResponseEntity.ok().body(usersService.create(crateDTO));
+    }
+
+    @GetMapping("/{id}")
+    public ResponseEntity<UserDTO> getById(@PathVariable UUID id) {
+        return ResponseEntity.ok().body(usersService.getById(id));
+    }
+
+    @GetMapping("/username/{username}")
+    public ResponseEntity<UserDTO> getByUsername(@PathVariable String username) {
+        return ResponseEntity.ok().body(usersService.getByUsername(username));
+    }
+
+    @GetMapping("/email/{email}")
+    public ResponseEntity<UserDTO> getByEmail(@PathVariable String email) {
+        return ResponseEntity.ok().body(usersService.getByEmail(email));
+    }
+
+    @GetMapping
+    public ResponseEntity<List<UserDTO>> getAll() {
+        return ResponseEntity.ok().body(usersService.getAll());
+    }
+
+    @PutMapping("/{id}")
+    public ResponseEntity<UserDTO> update(@PathVariable UUID id, @RequestBody @Valid NewUserDTO updateDTO) throws IllegalAccessException {
+        return ResponseEntity.ok().body(usersService.update(id, updateDTO));
+    }
+
+    @DeleteMapping("/{id}")
+    public ResponseEntity<Void> delete(@PathVariable UUID id) {
+        usersService.delete(id);
+        return ResponseEntity.noContent().build();
+    }
+}
diff --git a/backend/src/main/java/com/hitcommunications/servermanager/mappers/UsersMapper.java b/backend/src/main/java/com/hitcommunications/servermanager/mappers/UsersMapper.java
new file mode 100644
index 0000000..ce2b505
--- /dev/null
+++ b/backend/src/main/java/com/hitcommunications/servermanager/mappers/UsersMapper.java
@@ -0,0 +1,21 @@
+package com.hitcommunications.servermanager.mappers;
+
+import com.hitcommunications.servermanager.model.Users;
+import com.hitcommunications.servermanager.model.dtos.NewUserDTO;
+import com.hitcommunications.servermanager.model.dtos.UserDTO;
+import org.mapstruct.BeanMapping;
+import org.mapstruct.Mapper;
+import org.mapstruct.MappingTarget;
+import org.mapstruct.NullValuePropertyMappingStrategy;
+
+import java.util.List;
+
+@Mapper(componentModel = "spring", nullValuePropertyMappingStrategy = NullValuePropertyMappingStrategy.IGNORE)
+public interface UsersMapper {
+    Users toEntity(NewUserDTO createDTO);
+    UserDTO toDTO(Users entity);
+    List<Users> toDTO(List<Users> entities);
+
+    @BeanMapping(nullValuePropertyMappingStrategy = NullValuePropertyMappingStrategy.IGNORE)
+    Users partialUpdate(NewUserDTO updateDTO, @MappingTarget Users entity);
+}
diff --git a/backend/src/main/java/com/hitcommunications/servermanager/model/Users.java b/backend/src/main/java/com/hitcommunications/servermanager/model/Users.java
index 7e58c17..a0c78e8 100644
--- a/backend/src/main/java/com/hitcommunications/servermanager/model/Users.java
+++ b/backend/src/main/java/com/hitcommunications/servermanager/model/Users.java
@@ -58,6 +58,6 @@ public class Users {
         String firstPart = this.firstName != null && this.firstName.length() >= 3 ? this.firstName.substring(0, 3) : (this.firstName != null ? this.firstName : "");
         String secondPart = this.lastName != null && this.lastName.length() >= 3 ? this.lastName.substring(0, 3) : (this.lastName != null ? this.lastName : "");
         this.username = firstPart + secondPart;
-        return this.username;
+        return this.username.toLowerCase();
     }
 }
diff --git a/backend/src/main/java/com/hitcommunications/servermanager/model/dtos/NewUserDTO.java b/backend/src/main/java/com/hitcommunications/servermanager/model/dtos/NewUserDTO.java
new file mode 100644
index 0000000..99de0b4
--- /dev/null
+++ b/backend/src/main/java/com/hitcommunications/servermanager/model/dtos/NewUserDTO.java
@@ -0,0 +1,12 @@
+package com.hitcommunications.servermanager.model.dtos;
+
+import jakarta.validation.constraints.Email;
+import jakarta.validation.constraints.NotBlank;
+
+public record NewUserDTO(
+        @NotBlank String firstName,
+        @NotBlank String lastName,
+        @NotBlank  @Email String email,
+        @NotBlank String password
+) {
+}
diff --git a/backend/src/main/java/com/hitcommunications/servermanager/model/dtos/UserDTO.java b/backend/src/main/java/com/hitcommunications/servermanager/model/dtos/UserDTO.java
new file mode 100644
index 0000000..348984f
--- /dev/null
+++ b/backend/src/main/java/com/hitcommunications/servermanager/model/dtos/UserDTO.java
@@ -0,0 +1,15 @@
+package com.hitcommunications.servermanager.model.dtos;
+
+import java.sql.Timestamp;
+
+public record UserDTO(
+        String id,
+        String username,
+        String firstName,
+        String lastName,
+        String email,
+        Timestamp createdAt,
+        Timestamp updatedAt,
+        Timestamp lastLogin
+) {
+}
diff --git a/backend/src/main/java/com/hitcommunications/servermanager/repositories/UsersRepository.java b/backend/src/main/java/com/hitcommunications/servermanager/repositories/UsersRepository.java
new file mode 100644
index 0000000..7f59dd2
--- /dev/null
+++ b/backend/src/main/java/com/hitcommunications/servermanager/repositories/UsersRepository.java
@@ -0,0 +1,12 @@
+package com.hitcommunications.servermanager.repositories;
+
+import com.hitcommunications.servermanager.model.Users;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+import java.util.Optional;
+import java.util.UUID;
+
+public interface UsersRepository extends JpaRepository<Users, UUID> {
+ Optional<Users> findByUsername(String username);
+ Optional<Users> findByEmail(String email);
+}
diff --git a/backend/src/main/java/com/hitcommunications/servermanager/services/UsersService.java b/backend/src/main/java/com/hitcommunications/servermanager/services/UsersService.java
new file mode 100644
index 0000000..8c391d8
--- /dev/null
+++ b/backend/src/main/java/com/hitcommunications/servermanager/services/UsersService.java
@@ -0,0 +1,94 @@
+package com.hitcommunications.servermanager.services;
+
+import com.hitcommunications.servermanager.mappers.UsersMapper;
+import com.hitcommunications.servermanager.model.Users;
+import com.hitcommunications.servermanager.model.dtos.NewUserDTO;
+import com.hitcommunications.servermanager.model.dtos.UserDTO;
+import com.hitcommunications.servermanager.repositories.UsersRepository;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.UUID;
+
+@Service
+@RequiredArgsConstructor
+public class UsersService {
+    private final UsersMapper mapper;
+    private final UsersRepository repo;
+
+    private final String ALLOWED_DOMAIN = Arrays.asList("hittelco.com", "accesscommunications.com").toString();
+
+    public UserDTO create(NewUserDTO createDTO) throws IllegalAccessException {
+       String domain = getDomain(createDTO.email());
+       if (!ALLOWED_DOMAIN.contains(domain)) {
+           throw new IllegalAccessException("Email domain not allowed: " + domain);
+       }
+
+       repo.findByEmail(createDTO.email()).ifPresent(entity -> {
+           throw new RuntimeException("Email already exists: " + createDTO.email());
+       });
+
+        Users entity = mapper.toEntity(createDTO);
+        entity = repo.save(entity);
+        return mapper.toDTO(entity);
+    }
+
+    public UserDTO getById(UUID id) {
+        return repo.findById(id)
+                .map(mapper::toDTO)
+                .orElseThrow(() -> new RuntimeException("User not found with id: " + id));
+    }
+
+    public UserDTO getByUsername(String username) {
+        return repo.findByUsername(username)
+                .map(mapper::toDTO)
+                .orElseThrow(() -> new RuntimeException("User not found with username: " + username));
+    }
+
+    public UserDTO getByEmail(String email) {
+        return repo.findByEmail(email)
+                .map(mapper::toDTO)
+                .orElseThrow(() -> new RuntimeException("User not found with email: " + email));
+    }
+
+    public List<UserDTO> getAll() {
+        return repo.findAll()
+                .stream()
+                .map(mapper::toDTO)
+                .toList();
+    }
+
+    public UserDTO update(UUID id, NewUserDTO updateDTO) throws IllegalAccessException {
+        Users entity = repo.findById(id)
+                .orElseThrow(() -> new RuntimeException("User not found with id: " + id));
+
+        String domain = getDomain(updateDTO.email());
+        if (!ALLOWED_DOMAIN.contains(domain)) {
+            throw new IllegalAccessException("Email domain not allowed: " + domain);
+        }
+
+        // Check if email already exists (excluding current user)
+        repo.findByEmail(updateDTO.email()).ifPresent(existingUser -> {
+            if (!existingUser.getId().equals(id)) {
+                throw new RuntimeException("Email already exists: " + updateDTO.email());
+            }
+        });
+
+        mapper.partialUpdate(updateDTO, entity);
+        entity = repo.save(entity);
+        return mapper.toDTO(entity);
+    }
+
+    public void delete(UUID id) {
+        if (!repo.existsById(id)) {
+            throw new RuntimeException("User not found with id: " + id);
+        }
+        repo.deleteById(id);
+    }
+
+    private String getDomain(String email) {
+        return email.substring(email.indexOf("@") + 1);
+    }
+}