Input type email required is not working

Hello! Why does the e-mail field valid even it’s filled without domain? The field has a required attribute. If i specify an address, for example, “sdfdfg”, I get an error, but if “sdfdfg@sdfdfg” – the field is valid.
“Required” is always worked fine in any form. This is the first time I’ve seen this happen in this plugin. Does anyone know how to fix it?