fix: add backend validation for livechat offline message recipient

Author: mdawoud27

apps/meteor/app/livechat/server/lib/messages.ts

@@ -65,10 +65,6 @@ export async function sendOfflineMessage(data: OfflineMessageData) {
 		}
 	}
 
-	// TODO Block offline form if Livechat_offline_email is undefined
-	// (it does not make sense to have an offline form that does nothing)
-	// `this.sendEmail` will throw an error if the email is invalid
-	// thus this breaks livechat, since the "to" email is invalid, and that returns an [invalid email] error to the livechat client
 	let emailTo = settings.get<string>('Livechat_offline_email');
 	if (department && department !== '') {
 		const dep = await LivechatDepartment.findOneByIdOrName(department, { projection: { email: 1 } });
@@ -77,6 +73,10 @@ export async function sendOfflineMessage(data: OfflineMessageData) {
 		}
 	}
 
+	if (!emailTo) {
+		throw new Error('error-no-email-configured-to-receive-offline-messages');
+	}
+
 	const fromText = `${name} - ${email} <${from}>`;
 	const replyTo = `${name} <${email}>`;
 	const subject = `Livechat offline message from ${name}: ${`${emailMessage}`.substring(0, 20)}`;