diff --git a/modules/auth/user_form.go b/modules/auth/user_form.go
index 80af8e72d8..bc826c6915 100644
--- a/modules/auth/user_form.go
+++ b/modules/auth/user_form.go
@@ -30,7 +30,7 @@ type InstallForm struct {
 
 	SMTPHost        string
 	SMTPFrom        string
-	SMTPEmail       string `binding:"OmitEmpty;Email;MaxSize(50)" locale:"install.mailer_user"`
+	SMTPEmail       string `binding:"OmitEmpty;Email;MaxSize(254)" locale:"install.mailer_user"`
 	SMTPPasswd      string
 	RegisterConfirm bool
 	MailNotify      bool
@@ -44,7 +44,7 @@ type InstallForm struct {
 	AdminName          string `binding:"OmitEmpty;AlphaDashDot;MaxSize(30)" locale:"install.admin_name"`
 	AdminPasswd        string `binding:"OmitEmpty;MaxSize(255)" locale:"install.admin_password"`
 	AdminConfirmPasswd string
-	AdminEmail         string `binding:"OmitEmpty;MinSize(3);MaxSize(50);Include(@)" locale:"install.admin_email"`
+	AdminEmail         string `binding:"OmitEmpty;MinSize(3);MaxSize(254);Include(@)" locale:"install.admin_email"`
 }
 
 func (f *InstallForm) Validate(ctx *macaron.Context, errs binding.Errors) binding.Errors {