To enable the new email address validation feature (preview), log in to Power Platform Admin Center >> Settings >> Features >> Data Validation
Switch On – Data Validation. (Interestingly in one of the environments enabling this setting was enough to get the smart email validation working however in another environment had to enable the below settings as well to get that working)
Next open the Model Driven App in Maker Portal – App Designer and switch on Enable Smart Email Address Validation Control
Below we can see it validating the email address while we enter its value
We get the below messages
And this works for the email field in a custom entity as well.
Refer – https://learn.microsoft.com/en-us/power-apps/maker/data-platform/data-validation-email-column
Also, check the similar feature we have for Sales Hub App
Hope it helps..