Webform cache the emails submissions

Problem/Motivation

One user submit a webform and webform send an email (configured from /node/__NID__/webform/emails), this email are cached in cache_form table.

If the webform is a multistep form, in every step the email is stored in cache_form with the id form_state_form-****

A 5 steps webform generate 10 elements in the table. 5 for steps and 5 with the same rendered email template.

This make that the size of this table increment very fast. How can i prevent that those emails be cached?

Thanks!