ID  TIMESTAMP            TASK_ID
1   2019-01-30 15:29:38  1
2   2019-01-30 15:29:39  1
3   2019-01-30 15:29:40  2
4   2019-01-30 15:29:41  3

ID  EMAIL
1   boxOne@test.com
2   boxOne@test.com
3   boxTwo@test.com

SELECT TASK.id, TASK.EMAIL, count(att.TASK_ID)
FROM TASK
JOIN ATTEMPTS on TASK.id = ATTEMPTS.TASK_ID
GROUP BY ATTEMPTS.TASK_ID

TASK.id  EMAIL            count(TASK.id)
1        boxOne@test.com  2
2        boxOne@test.com  1
3        boxTwo@test.com  1

TASK.id  EMAIL            count(TASK.id)
2        boxOne@test.com  1
3        boxTwo@test.com  1

select distinct t1.* from
(
SELECT TASK.id, TASK.EMAIL, count(att.TASK_ID) cnt
FROM TASK
JOIN ATTEMPTS on TASK.id = ATTEMPTS.TASK_ID
) t1 where t1.cnt= (select min(cnt) from
                       (SELECT TASK.id, TASK.EMAIL, count(att.TASK_ID) cnt
                       FROM TASK
                       JOIN ATTEMPTS on TASK.id = ATTEMPTS.TASK_ID
                       ) t2 where t2.EMAIL=t1.EMAIL)