Curently, the '1' value is set for that 'SendEMail' parameter in SagePay payment option in Ecwid. Unfortunately, there is no way to change it yet. Please add an idea to our ideas base
and we will implement this improvement as soon as it get enough votes.
Meanwhile, you can consider a workaround - you can develop a custom payment option and use it with your Ecwid store. Since any payment method can be integrated with Ecwid by means of our Custom Payment Gateways API, you can integrate SagePay including the desired changes. Please read the following article for the details:
If you need help with development of such a solution, you can contact our friends from Qualiteam. Please refer to this page for the details: