diff --git a/modoboa/core/app_settings.py b/modoboa/core/app_settings.py
index 773d5b315..5d4ea3ce8 100644
--- a/modoboa/core/app_settings.py
+++ b/modoboa/core/app_settings.py
@@ -285,8 +285,6 @@ class GeneralParametersForm(parameters.AdminParametersForm):
         required parameters.
         """
         super(GeneralParametersForm, self).clean()
-        if len(self._errors):
-            raise forms.ValidationError(self._errors)
         cleaned_data = self.cleaned_data
         if cleaned_data["authentication_type"] != "ldap":
             return cleaned_data
@@ -298,8 +296,7 @@ class GeneralParametersForm(parameters.AdminParametersForm):
 
         for f in required_fields:
             if f not in cleaned_data or cleaned_data[f] == u'':
-                self._errors[f] = self.error_class(
-                    [_("This field is required")])
+                self.add_error(f, _("This field is required"))
 
         return cleaned_data
 
diff --git a/modoboa/extensions/admin/forms/account.py b/modoboa/extensions/admin/forms/account.py
index 37d70964b..1b3ef6b10 100644
--- a/modoboa/extensions/admin/forms/account.py
+++ b/modoboa/extensions/admin/forms/account.py
@@ -208,14 +208,10 @@ class AccountFormMail(forms.Form, DynamicForm):
         Check if quota is >= 0 only when the domain value is not used.
         """
         super(AccountFormMail, self).clean()
-        if self._errors:
-            raise forms.ValidationError(self._errors)
         if not self.cleaned_data["quota_act"] \
                 and self.cleaned_data['quota'] is not None:
             if self.cleaned_data["quota"] < 0:
-                self._errors["quota"] = self.error_class(
-                    [_("Must be a positive integer")])
-                del self.cleaned_data["quota"]
+                self.add_error("quota", _("Must be a positive integer"))
         return self.cleaned_data
 
     def create_mailbox(self, user, account):
diff --git a/modoboa/extensions/admin/forms/domain.py b/modoboa/extensions/admin/forms/domain.py
index 45bf1149e..359e2d000 100644
--- a/modoboa/extensions/admin/forms/domain.py
+++ b/modoboa/extensions/admin/forms/domain.py
@@ -78,18 +78,13 @@ class DomainFormGeneral(forms.ModelForm, DynamicForm):
         The validation way is not very smart...
         """
         super(DomainFormGeneral, self).clean()
-        if self._errors:
-            raise forms.ValidationError(self._errors)
-
         cleaned_data = self.cleaned_data
         name = cleaned_data["name"]
         label = check_if_domain_exists(name, [(DomainAlias, _('domain alias'))])
         if label is not None:
-            self._errors["name"] = self.error_class(
-                [_("A %s with this name already exists" % unicode(label))]
+            self.add_error(
+                "name", _("A %s with this name already exists") % unicode(label)
             )
-            del cleaned_data["name"]
-
         for k in cleaned_data.keys():
             if not k.startswith("aliases"):
                 continue
@@ -99,11 +94,8 @@ class DomainFormGeneral(forms.ModelForm, DynamicForm):
             label = check_if_domain_exists(
                 cleaned_data[k], [(Domain, _('domain'))])
             if label is not None:
-                self._errors[k] = self.error_class(
-                    [_("A %s with this name already exists" % unicode(label))]
-                )
-                del cleaned_data[k]
-
+                self.add_error(
+                    k, _("A %s with this name already exists") % unicode(label))
         return cleaned_data
 
     def update_mailbox_quotas(self, domain):
diff --git a/modoboa/extensions/limits/forms.py b/modoboa/extensions/limits/forms.py
index 0f0b27f9a..b96d10ef3 100644
--- a/modoboa/extensions/limits/forms.py
+++ b/modoboa/extensions/limits/forms.py
@@ -37,8 +37,7 @@ class ResourcePoolForm(forms.Form):
         cleaned_data = super(ResourcePoolForm, self).clean()
         for lname in self.fields.keys():
             if lname not in self._errors and cleaned_data[lname] < -1:
-                self._errors[lname] = self.error_class([_('Invalid limit')])
-                del cleaned_data[lname]
+                self.add_error(lname, _("Invalid limit"))
         return cleaned_data
 
     def load_from_user(self, user):
diff --git a/modoboa/extensions/postfix_autoreply/forms.py b/modoboa/extensions/postfix_autoreply/forms.py
index 0e32ebf0d..2252672bf 100644
--- a/modoboa/extensions/postfix_autoreply/forms.py
+++ b/modoboa/extensions/postfix_autoreply/forms.py
@@ -63,26 +63,19 @@ class ARmessageForm(forms.ModelForm):
 
         """
         super(ARmessageForm, self).clean()
-        if self._errors:
-            raise forms.ValidationError(self._errors)
         if not self.cleaned_data["enabled"]:
             return self.cleaned_data
         if self.cleaned_data["fromdate"] is not None:
             if self.cleaned_data["fromdate"] < timezone.now():
-                self._errors["fromdate"] = self.error_class(
-                    [_("This date is over")])
-                del self.cleaned_data['fromdate']
+                self.add_error("fromdate", _("This date is over"))
         else:
             self.cleaned_data['fromdate'] = timezone.now()
         if self.cleaned_data["untildate"] is not None:
             untildate = self.cleaned_data["untildate"]
             if untildate < timezone.now():
-                self._errors["untildate"] = self.error_class(
-                    [_("This date is over")])
-                del self.cleaned_data["untildate"]
+                self.add_error("untildate", _("This date is over"))
             elif "fromdate" in self.cleaned_data and \
                     untildate < self.cleaned_data["fromdate"]:
-                self._errors["untildate"] = \
-                    self.error_class([_("Must be greater than start date")])
-                del self.cleaned_data["untildate"]
+                self.add_error(
+                    "untildate", _("Must be greater than start date"))
         return self.cleaned_data
diff --git a/modoboa/extensions/postfix_relay_domains/forms.py b/modoboa/extensions/postfix_relay_domains/forms.py
index 0fcd2535f..ddafe295d 100644
--- a/modoboa/extensions/postfix_relay_domains/forms.py
+++ b/modoboa/extensions/postfix_relay_domains/forms.py
@@ -55,8 +55,6 @@ class RelayDomainFormGeneral(forms.ModelForm, DynamicForm):
         The validation way is not very smart...
         """
         super(RelayDomainFormGeneral, self).clean()
-        if self._errors:
-            raise forms.ValidationError(self._errors)
         cleaned_data = self.cleaned_data
         for dtype, label in [(Domain, _('domain')),
                              (DomainAlias, _('domain alias')),
@@ -66,10 +64,9 @@ class RelayDomainFormGeneral(forms.ModelForm, DynamicForm):
             except dtype.DoesNotExist:
                 pass
             else:
-                self._errors["name"] = self.error_class(
-                    [_("A %s with this name already exists" % label)]
+                self.add_error(
+                    "name", _("A %s with this name already exists") % label
                 )
-                del cleaned_data["name"]
                 break
 
         for k in cleaned_data.keys():
@@ -86,10 +83,8 @@ class RelayDomainFormGeneral(forms.ModelForm, DynamicForm):
                 except dtype.DoesNotExist:
                     pass
                 else:
-                    self._errors[k] = self.error_class(
-                        [_("A %s with this name already exists" % name)]
-                    )
-                    del cleaned_data[k]
+                    self.add_error(
+                        k, _("A %s with this name already exists") % name)
                     break
 
         return cleaned_data