This is great. I've used https://formspree.io before, but it was a headache to obfuscate the emails, so your alias functionality looks awesome. Do you have any sending limits and/or future plans for monetizing the service?
Future plans to monetize may include saved messages (which I'm not to keen on), multiple alias' or alias forwarding, the custom fields may or may not be monetized. I may go the Patreon route and if people like the service they can pay what they want.