diff --git a/EnvelopeGenerator.Web/Views/Home/ShowEnvelope.cshtml b/EnvelopeGenerator.Web/Views/Home/ShowEnvelope.cshtml
index eac905dc..62ff4ec7 100644
--- a/EnvelopeGenerator.Web/Views/Home/ShowEnvelope.cshtml
+++ b/EnvelopeGenerator.Web/Views/Home/ShowEnvelope.cshtml
@@ -159,6 +159,16 @@
         const receiverMail_value = receiverMail.value;
         const dateValid_value = dateValid.value;
     
+        //check email
+        if (!dateValid.classList.contains('is-invalid')) {
+            Swal.fire({
+                icon: "error",
+                title: "Falsche Email",
+                text: "Die E-Mail-Adresse ist ungültig. Bitte verwenden Sie das richtige Format, z. B.: user@mail.com."
+            });
+            return;
+        }
+
         //check the date
         const tomorrow = new Date(Date.now() + 86400000);
         if (new Date(dateValid_value) < tomorrow) {