About daily counts & NetWallah's proposal: Alas the (rather arbitrary) problem constraints include a table that has no time/date- it only has one column "addr" for email addresses. I assume that it grows continually.

So for the daily count, have the program run once a day- the same program that counts the # of domains can also count how many rows are in the table, and store it (in a file, or in the database, whatever is allowed). Then on the next run it can subtract to find the number of new records. That matches the Anonymous Monk's earlier suggestion.

In fact, you could make the program more efficient- though more complicated- by also storing the domain count, and re-reading it on startup, then skipping over the old records on the next run. Then you only need to add up the new domains, and add those to the old totals. That will only work if addresses are returned in the order they are created! If you go that way, document that assumption!