Actually, If you are arriving into T at ATL, then you will pre-clear customs and imigration in Canada. T concourse no longer has INS and Customs facilities.

The train is quite rapid from T to E. You should be able to make your connection in about 30 to 45 minutes.

With an international DL business class/First Class ticket, you should get access to the Business Class lounge in E concourse.

Have a nice trip.