feat: add empty emails for envelopes

packages/lib/utils/recipients.ts

@@ -1,5 +1,6 @@
 import type { Envelope } from '@prisma/client';
 import { type Field, type Recipient, RecipientRole, SigningStatus } from '@prisma/client';
+import { z } from 'zod';
 
 import { NEXT_PUBLIC_WEBAPP_URL } from '../constants/app';
 import { extractLegacyIds } from '../universal/id';
@@ -58,3 +59,7 @@ export const mapRecipientToLegacyRecipient = (
     ...legacyId,
   };
 };
+
+export const isRecipientEmailValidForSending = (recipient: Pick<Recipient, 'email'>) => {
+  return z.string().email().safeParse(recipient.email).success;
+};