More work on post registration form

frontend-reactive/app/helpers/is-valid-mail.ts

@@ -0,0 +1,14 @@
+import { helper } from '@ember/component/helper';
+
+const re = /.+@\S+\.\S+/;
+
+// Helper to check if a given email is *probably* valid
+// Ofc, the only surefire way to check if an email exists is to send a test mail to it.
+// This sending is expensive however, and thus some mostly sane defaults can be checked for
+// beforehand. "Bananentürkis" for example is obviously not a valid address
+export default helper(function isValidMail(positional: string[] /*, named*/) {
+  for (const mail of positional) {
+    if (!re.test(mail)) return false;
+  }
+  return true;
+});