Report to sum all customer transactions by month

Hello everybody, completely new here. I tried searching for a solution many hours and just couldn't find any, so I decided to ask for help.

So I have monthly reports of my customers and I need to know how much every customer spent in the whole year.

I imagine that first I would need to create a new sheet and with some unknown formula to me to get all unique customer emails first.
And then next to it with another unknown formula to sum all the transactions from my original reports with customer email X.

Can you help me figuring out these two formulas?
Thanks in advance!

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