T-SQL (SS2K8) :: Agent Job Report Omit Previously Sent Data

I have this report i setup as an agent job in SSMS; It's setup to run every 7 minutes and it only sends the report if data is present. I'd like to add the ability to omit any rows that were sent in the previous report.

This is what the script looks like:

if exists (select o.ord_billto, o.ord_refnum , o.ord_hdrnumber, o.mov_number, o.ord_status, o.ord_cmdvalue, o.ord_startdate
from orderheader o
where ord_billto in ('A','B','C','D')
and DATEDIFF(minute , o.ord_datetaken, GETDATE())<=7

[Code] ....

Also, why I can't seem to use IF ( Select [...]) > 0? When i try using that instead of IF EXISTS i get this error: "Msg 116, Level 16, State 1, Line 7
Only one expression can be specified in the select list when the subquery is not introduced with EXISTS."