How to define the recipient for "Send Direct Email"

Hi,

I'm trying to change the recipient from an email sent with "Send Direct Email" on an Opportunity.

Today the Company linked to the opportunity is used, I would like for the Contact to be used.

I tried the mappings but I can't map the fields.

I tried a Workflow but it's not executing quickly enough to do the change, even if I set it as a real time workflow or make it execute before the status of the email changes from Draft to Sent.

Thanks!