You have a couple of options:
- Tag each link to your landing page with the proper field names.
Most email clients would allow you to tag your URLs this way and fill out the variables automatically. If you customers are coming from an internal page/link rather than an email campaign, you'll need to modify the link to include the above information and pass it on to the landing page.
When one of your customers clicks on such a link and they are taken to the landing page, all of that information in the URL would be auto-filled in your form.