SUM or COUNT in Report


I have a question about the report function.

What is the difference between SUM and COUNT and when do I use which? Is it like in Excel?

I tried it with the “bounced”-collumn and got different results. With “SUM” it shows 0, with “COUNT” I got a realistic number.

But when I try it with “unsubscribe” it is the other way arround. SUM = realistic number, and COUNT = 0.

Also the loading time for the report is long and sometimes crashes our system.
Example: I want a report of all mails from one month (ca. 50 emails with ~20.000 contacts)

Is it possible to speed it up without reducing the output,