Forms: How to make the optional fields more subtle to reduce their use?

How to make optional fields such as email a bit more subtle? The intention is to have a minimum prominence for the email field and reduce its use. The reason why we can not eliminate it is that customers decide the capture fields of potential customers and force us to keep it optional instead of eliminating it.

There are 2 options we have:

with open text email field

two) The image below has been labeled as an email, but we will keep it as an email (optional). It is a check box that will open the text entry similar to the first image:
with check box - which opens the text field once it is clicked

Which of the two options is better in terms of:

1) More people should understand that it is optional and omit it if they wish.
2) wise user experience