If you want to send an end user who completes a Workflow an email you can do this via an integration.
We currently offer a direct Mandrill integration and there are lots of options via Zapier.
The reason for this approach is that you are likely to want to send a branded email to your Workflow form filler and you are likely to want to send it from your own email address. Because of this it's better to pass the data through from Malcolm! to an account you have with a transactional email service where you have set up SPF and DKIM etc to ensure deliverability. They also offer a whole load of functionality it doesn't make sense for us to replicate our side.