How to connect a domain email?

You can not create your own domain email on Tilda, unfortunately. If your domain has been delegated to Tilda, you can create an email in a third-party service and specify TXT and MX records in the domain management panel.

A detailed guide on adding TXT and MX records is at this link: https://help.tilda.cc/tilda-dns#records 

How to create the domain email in a third-party service: https://help.tilda.cc/mail-domain