diff --git a/src/services/user.service.ts b/src/services/user.service.ts
index 52ae207..a885123 100644
--- a/src/services/user.service.ts
+++ b/src/services/user.service.ts
@@ -1,10 +1,14 @@
-import type { IReqLogin } from "@interfaces/requests/IReqLogin";
-import type { IReqRegister } from "@interfaces/requests/IReqRegister";
+import type {IDbUser} from "@interfaces/database/IDbUser";
+import type {IReqLogin} from "@interfaces/requests/IReqLogin";
+import type {IReqRegister} from "@interfaces/requests/IReqRegister";
+import {ErrorType, type ISError} from "@interfaces/services/ISError";
 import CredentialService from "@services/credential.service";
 import JwtService from "@services/jwt.service";
 import MySqlService from "@services/mysql.service";
 import MysqlService from "@services/mysql.service";
-import { Logger } from "tslog";
+import {Logger} from "tslog";
+import {v4} from "uuid";
+
 
 const logger = new Logger({
 	name: "UserService",
@@ -13,92 +17,124 @@ const logger = new Logger({
 const DbHandler = new MySqlService.Handler("UserService");
 
 /**
- * Retrieves a user object from the database based on the given username.
+ * Retrieves a user from the database by the given email address.
  *
- * @param {string} username - The username of the user to retrieve.
- * @returns {Promise<Object | null>} - The user object if found, or null if not found.
+ * @param {string} targetEmail - The email address of the user to retrieve.
+ * @returns {Promise<IDbUser | ISError>}
+ * 			- A promise that resolves with the user.
+ *   		- If the user is not found, an error object is returned.
+ *   		- If an error occurs during the database operation, an error object is returned.
  */
-async function getUserFromUsername(username: string): Promise<object | null> {
-	const dbUser = await MySqlService.User.getByUsername(DbHandler, username);
-	if (dbUser === undefined) return null;
-	return dbUser;
-}
-
-async function getUserFromIdService(id: string | undefined) {
-	const dbUser = await MySqlService.User.getById(DbHandler, id);
-	if (dbUser === undefined) return null;
-	return dbUser;
-}
-
-async function register(ReqData: IReqRegister) {
-	if (ReqData.password.length < 6) {
-		logger.info(`REGISTER :> Invalid password (${ReqData.username})`);
+async function getUserByEmail(targetEmail: string): Promise<IDbUser | ISError> {
+	try {
+		const dbUser = await MySqlService.User.getByEmail(DbHandler, targetEmail);
+		if (dbUser === undefined) {
+			logger.info(`User not found (${targetEmail})`);
+			return {
+				error: ErrorType.NotFound,
+				message: "The user was not fund.",
+			};
+		}
+		return dbUser;
+	} catch (err) {
+		logger.error(err);
 		return {
-			error: "invalidPassword",
+			error: ErrorType.DatabaseError,
+			message: "An unknown error occurred.",
 		};
 	}
-	const passwordHash = await CredentialService.hash(ReqData.password);
+}
+
+/**
+ * Retrieves a user from the database based on the provided ID.
+ *
+ * @param {string} id - The ID of the user to retrieve.
+ * @returns {Promise<IDbUser | ISError>} - A promise that resolves with the user object if found, or an error object if not.
+ */
+async function getUserFromIdService(id: string): Promise<IDbUser | ISError> {
+	try {
+		if (!id || id.length !== 36) {
+			logger.info(`Invalid ID (${id})`);
+			return {
+				error: ErrorType.InvalidData,
+				message: "Invalid ID length.",
+			};
+		}
+		const dbUser = await MySqlService.User.getById(DbHandler, id);
+		if (dbUser === undefined) {
+			logger.info(`User not found (${id})`);
+			return {
+				error: ErrorType.NotFound,
+				message: "The user was not found.",
+			};
+		}
+		return dbUser;
+	} catch (err) {
+		return {
+			error: ErrorType.DatabaseError,
+			message: "An unknown error occurred.",
+		};
+	}
+}
+
+async function register(ReqData: IReqRegister): Promise<ISError | string> {
+	if (ReqData.password.length < 6) {
+		return {
+			error: ErrorType.InvalidData,
+			message: "Password must be at least 6 characters long.",
+		};
+	}
+	const passwordHash = await CredentialService.hash(`${ReqData.password}`);
 
 	// Does the new user has accepted GDPR ?
 	if (ReqData.gdpr !== true) {
-		logger.info(`REGISTER :> GDPR not validated (${ReqData.username})`);
 		return {
-			error: "gdprNotApproved",
+			error: ErrorType.InvalidData,
+			message: "GDPR acceptance is required.",
 		};
 	}
-
-	// Check if exist and return
-
-	const dbUserIfExist = await getUserFromUsername(ReqData.username);
-	if (dbUserIfExist) {
-		logger.info(
-			`REGISTER :> User exist (${dbUserIfExist.username})\n ID:${dbUserIfExist.id}`,
-		);
-		return {
-			error: "exist",
-		};
-	}
-
 	const currentDate = new Date();
 
-	// New UserService (class)
+	// Check if exist and return
+	const dbUserIfExist: IDbUser | ISError = await getUserByEmail(ReqData.email);
+	if ("error" in dbUserIfExist) {
+		return {
+			error: dbUserIfExist.error,
+			message: dbUserIfExist.message,
+		};
+	}
 
-	const NewUser = new User(
-		ReqData.username,
-		ReqData.displayName,
-		passwordHash,
-		currentDate,
-	);
-	NewUser.setFirstName(ReqData.firstName);
-	NewUser.setLastName(ReqData.lastName);
+	const NewUser = await MySqlService.User.insert(DbHandler, {
+		id: v4(),
+		email: ReqData.email,
+		username: ReqData.username,
+		firstname: ReqData.firstName,
+		lastname: ReqData.lastName,
+		dob: ReqData.dob,
+		hash: passwordHash,
+		gdpr: currentDate,
+		is_admin: false,
+		is_mail_verified: false,
+	});
+	if ("error" in NewUser || !NewUser.id) {
+    return {
+      error: ErrorType.DatabaseError,
+			message: 'Error when inserting user in database.'
+    };
+  }
 
 	// JWT
-
-	const alg = "HS512";
 	const token = await JwtService.sign(
 		{
 			sub: NewUser.id,
 		},
-		alg,
+		{
+			alg: "HS512",
+		},
 		"1d",
 		"user",
 	);
-
-	const userData = {
-		error: "none",
-		jwt: token,
-		user: {
-			id: NewUser.id,
-			username: NewUser.username,
-			displayName: NewUser.displayName,
-			firstName: NewUser.firstName,
-			lastName: NewUser.lastName,
-		},
-	};
-	logger.info(userData);
-	await Db.collection("users").insertOne(NewUser);
-	logger.info(`REGISTER :> Inserted new user (${NewUser.username})`);
-	return userData;
+	return token;
 }
 
 async function login(ReqData: IReqLogin) {