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