SELECT id, payer_email
FROM paypal_ipn_orders
WHERE payer_email IN (
SELECT payer_email
FROM paypal_ipn_orders
GROUP BY payer_email
HAVING COUNT(id) > 1
)
sqlfiddle
SELECT id, payer_email
FROM paypal_ipn_orders
WHERE payer_email IN (
SELECT payer_email
FROM paypal_ipn_orders
GROUP BY payer_email
HAVING COUNT(id) > 1
)