Email ID formatting

DECLARE @emailAddress NVARCHAR(100) = 'HelloWorld@gmail.com'

DECLARE @Prefix NVARCHAR(100)
DECLARE @DomainName NVARCHAR(100)

SET @Prefix = LEFT(@emailAddress, CHARINDEX('@', @emailAddress) - 1)
SET @DomainName = RIGHT(@emailAddress, CHARINDEX('@', @emailAddress) - 2)

--Assuming that prefix of email address is always 5 more chatacters
DECLARE @PrefixStart NVARCHAR(100)
DECLARE @PrefixEnd NVARCHAR(100)

SELECT @PrefixStart = SUBSTRING (@Prefix, 1 , 2)
SELECT @PrefixEnd = SUBSTRING (@Prefix, LEN(@Prefix) - 1 , LEN(@Prefix))

SELECT @PrefixStart + REPLICATE('*', LEN(SUBSTRING (@Prefix, 3 , LEN(@Prefix) - 3))) + @PrefixEnd + '@' + @DomainName

using System;

public class Program
{
    public static void Main()
    {
        string email_id = "sontosh_kumar_rch@yahoo.com";

        int pos = email_id.IndexOf("@");

        if (email_id.IndexOf("@") != -1)
        {
            string left_part = email_id.Substring(0, pos);
            Console.WriteLine(left_part); // sontosh_kumar_rch

            string first_two = left_part.Substring(0, 2);
            Console.WriteLine(first_two);  // so

            string last_two = left_part.Substring(pos - 2);
            Console.WriteLine(last_two); // ch

            string right_part = email_id.Substring(pos);
            Console.WriteLine(right_part); // @yahoo.com

            string result = first_two + new String('.', pos - 4) + last_two + right_part;
            Console.WriteLine(result); // so.............ch@yahoo.com
        }
    }
}