Is it good practice to rely on domain constraints for validation

Is it good practice to rely on domain constraints for validation

Is it good practice to validate user input using the domain constraints
such as email(unique:true) then rely on a message.properties input such as
className.email.unique=Email address already in use to create an error
message. Or is it better practice to have some client side validation or
some check being carried in a web service before trying to persist to the
domain?