SELECT [ReportId],
SUBSTRING(d.EmailList,1, LEN(d.EmailList) - 1) EmailList
FROM
(
SELECT DISTINCT [ReportId]
FROM Table1
) a
CROSS APPLY
(
SELECT [Email] + ', '
FROM Table1 AS B
WHERE A.[ReportId] = B.[ReportId]
FOR XML PATH('')
) D (EmailList)