Thank you very much for your feedback, we've had many requests for this capability however Nintex will always require its own managed email service to process incoming express approval responses as well as ensuring all emails are reliably delivered.
Please note that you can already specify the senders display name however the actual from address will always be from workflowcloud.com
At this stage we are passing on this particular idea as it does not align with the core product mission and roadmap. We welcome additional ideas and feedback from you in the future.
It would be ideal to use our own domain especially with Cusotmers vs nintex@workflowcloud.com. Cusotmers think this is a suspicious email and delete them. Coming fomr our company email address appears more legit email.