This service should come with a big fat warning that the emoji email addresses should never be used for anything remotely serious. Running an email service is not, by any means, a 'tiny project'. I would never pay, nor rely on an e-mail service that is effectively a one-men side project. I just took a quick check on the 'mailbox' domain (I can't paste emoji here on HN). There seems to be no DMARC, no MTA-STS and no T…
TLS and MTA-STS are for receiving and would be good to set up, eventually.