To add expiry headers to your email, you will need to modify the email header section. This often requires technical expertise or the use of an Email Service Provider (ESP) that supports this feature. Here is a basic example:
Date: Tue, 19 Sep 2023 16:30:00 GMT From: sender@example.com To: recipient@example.com Subject: Limited Time Offer! Expiry-Date: Wed, 20 Oct 2023 18:30:00 GMT