diff --git a/backend/handlers/auth/local.go b/backend/handlers/auth/local.go
index dd88af9..f6f5b7f 100644
--- a/backend/handlers/auth/local.go
+++ b/backend/handlers/auth/local.go
@@ -14,7 +14,6 @@ import (
 	"fmt"
 	"log"
 	"net/http"
-	"net/mail"
 	"regexp"
 	"strings"
 	"sync"
@@ -136,9 +135,8 @@ func RegisterHandler(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Validate email format
-	_, err := mail.ParseAddress(req.Email)
-	if err != nil {
-		http.Error(w, "invalid email format", http.StatusBadRequest)
+	if err := validators.ValidateEmail(req.Email); err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
 		return
 	}
 
diff --git a/backend/handlers/bookings/bookings.go b/backend/handlers/bookings/bookings.go
index a35defe..41fbc48 100644
--- a/backend/handlers/bookings/bookings.go
+++ b/backend/handlers/bookings/bookings.go
@@ -687,7 +687,7 @@ func GetAllAdminBookingsHandler(w http.ResponseWriter, r *http.Request) {
 func GetAllBookingsByUserHandler(w http.ResponseWriter, r *http.Request) {
 	userID := chi.URLParam(r, "user_id")
 	if userID == "" || !validators.IsValidID(userID) {
-		http.Error(w, "User not found", http.StatusNotFound)
+		http.Error(w, "user not found", http.StatusNotFound)
 		return
 	}
 
diff --git a/backend/handlers/services/services.go b/backend/handlers/services/services.go
index f49774f..b42572e 100644
--- a/backend/handlers/services/services.go
+++ b/backend/handlers/services/services.go
@@ -398,7 +398,7 @@ func ServicesHandler(w http.ResponseWriter, r *http.Request) {
 func ServicesEligibleForUserHandler(w http.ResponseWriter, r *http.Request) {
 	userID := chi.URLParam(r, "user_id")
 	if userID == "" || !validators.IsValidID(userID) {
-		http.Error(w, "User not found", http.StatusNotFound)
+		http.Error(w, "user not found", http.StatusNotFound)
 		return
 	}
 
@@ -406,7 +406,7 @@ func ServicesEligibleForUserHandler(w http.ResponseWriter, r *http.Request) {
 	var dob time.Time
 	err := db.DB.QueryRow(r.Context(), `SELECT date_of_birth FROM users WHERE id = $1`, userID).Scan(&dob)
 	if errors.Is(err, sql.ErrNoRows) {
-		http.Error(w, "User not found", http.StatusNotFound)
+		http.Error(w, "user not found", http.StatusNotFound)
 		return
 	}
 	if err != nil {
diff --git a/backend/handlers/user/customer_relationship.go b/backend/handlers/user/customer_relationship.go
index cf34b59..387e71e 100644
--- a/backend/handlers/user/customer_relationship.go
+++ b/backend/handlers/user/customer_relationship.go
@@ -36,7 +36,7 @@ type TopService struct {
 func GetCustomerRelationshipHandler(w http.ResponseWriter, r *http.Request) {
 	userID := chi.URLParam(r, "id")
 	if userID == "" || !validators.IsValidID(userID) {
-		http.Error(w, "User not found", http.StatusNotFound)
+		http.Error(w, "user not found", http.StatusNotFound)
 		return
 	}
 
@@ -52,7 +52,7 @@ func GetCustomerRelationshipHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	if !exists {
-		http.Error(w, "User not found", http.StatusNotFound)
+		http.Error(w, "user not found", http.StatusNotFound)
 		return
 	}
 
diff --git a/backend/handlers/user/profile.go b/backend/handlers/user/profile.go
index 2704f0f..b3ddac7 100644
--- a/backend/handlers/user/profile.go
+++ b/backend/handlers/user/profile.go
@@ -301,7 +301,7 @@ func UpdateProfileHandler(w http.ResponseWriter, r *http.Request) {
 func GetAdminUserHandler(w http.ResponseWriter, r *http.Request) {
 	userID := chi.URLParam(r, "id")
 	if userID == "" || !validators.IsValidID(userID) {
-		http.Error(w, "User not found", http.StatusNotFound)
+		http.Error(w, "user not found", http.StatusNotFound)
 		return
 	}
 
@@ -330,7 +330,7 @@ func GetAdminUserHandler(w http.ResponseWriter, r *http.Request) {
 
 	if err != nil {
 		if errors.Is(err, sql.ErrNoRows) {
-			http.Error(w, "User not found", http.StatusNotFound)
+			http.Error(w, "user not found", http.StatusNotFound)
 			return
 		}
 		log.Printf("Failed to fetch user %s: %v", userID, err)
@@ -610,7 +610,7 @@ type ServiceForPatchTest struct {
 func GetEligiblePatchTestServicesHandler(w http.ResponseWriter, r *http.Request) {
 	userID := chi.URLParam(r, "id")
 	if userID == "" || !validators.IsValidID(userID) {
-		http.Error(w, "User not found", http.StatusNotFound)
+		http.Error(w, "user not found", http.StatusNotFound)
 		return
 	}
 
@@ -665,7 +665,7 @@ type AddPatchTestRequest struct {
 func AddPatchTestHandler(w http.ResponseWriter, r *http.Request) {
 	userID := chi.URLParam(r, "id")
 	if userID == "" || !validators.IsValidID(userID) {
-		http.Error(w, "User not found", http.StatusNotFound)
+		http.Error(w, "user not found", http.StatusNotFound)
 		return
 	}
 
@@ -726,7 +726,7 @@ type UserPatchTest struct {
 func GetUserPatchTestsHandler(w http.ResponseWriter, r *http.Request) {
 	userID := chi.URLParam(r, "user_id")
 	if userID == "" || !validators.IsValidID(userID) {
-		http.Error(w, "User not found", http.StatusNotFound)
+		http.Error(w, "user not found", http.StatusNotFound)
 		return
 	}
 
@@ -763,7 +763,7 @@ func DeletePatchTestHandler(w http.ResponseWriter, r *http.Request) {
 	userID := chi.URLParam(r, "user_id")
 	testID := chi.URLParam(r, "test_id")
 	if userID == "" || !validators.IsValidID(userID) {
-		http.Error(w, "User not found", http.StatusNotFound)
+		http.Error(w, "user not found", http.StatusNotFound)
 		return
 	}
 	if testID == "" || !validators.IsValidID(testID) {