ErcanOPAK.com

You can use query below:

DECLARE @Email     VARCHAR(50) = 'info@ercanopak.com'

SELECT SUBSTRING(@Email, 1, CHARINDEX('@', @Email) - 1) AS [User Name],
       SUBSTRING(@Email, CHARINDEX('@', @Email) + 1, LEN(@Email)) AS [Domain Name]

User Name   Domain Name
----------- -------------
info        ercanopak.com