Email
aaa@gmail.com
ccc@gmail.com
ddd@gmail.com
ccc@gmail.com
bbb@gmail.com
aaa@gmail.com

Email           Email_ID
aaa@gmail.com   001
ccc@gmail.com   002
ddd@gmail.com   003
ccc@gmail.com   002
bbb@gmail.com   004
aaa@gmail.com   001

SELECT
    Email,
    LPAD(CAST(DENSE_RANK() OVER (ORDER BY Email) AS CHAR(3)), '0', 3) AS Email_ID
FROM yourTable
ORDER BY
    Email;