Help optimizing DAX with SUMX and RELATEDTABLE

Hi everyone,

Here is the challenge.  I have a table of donors, and a related table of mailings to those donors.  I need to calculate the first-year cost of those mailings, on a per-donor basis (the cost of the mailings to each donor in the first year after each donor is added to the file).

I have some code that works, but I'm getting out of memory errors when I load in a few hundred million rows of data.  Is there a more efficient way to perform this calculation?

This is the calculated column:

_______________

Year1 Cost=
CALCULATE (
      SUMX (
          RELATEDTABLE ( Mailing ),
                 Mailing[Cost]
        ),
FILTER (
            RELATEDTABLE ( Mailing ),
             Mailing[MailDate]<= Donor[AddDate] + 365
    )
)

_______________

By the  way, I also have to calculate Year 2 and Year 3 costs, so the memory issue is compounded.

Thanks for any suggestions!

Dan