^([a-z0-9_\.]+)@([\da-z\.-]+)\.([a-z\.]{2,6})$
https://regex101.com/
https://regexper.com/
https://regexper.com/#%5E%28%5Ba-z0-9_%5C.%5D%2B%29%40%28%5B%5Cda-z%5C.-%5D%2B%29%5C.%28%5Ba-z%5C.%5D%7B2%2C6%7D%29%24