What is the benefit of temporary mail sites?

Question

Mail server

Drive "temporary mail" into Google, the first top links, there are no ads on them, how do they live then? Where is the profit from? What do they keep servers and eat?

Answer 1

There are ads and it's full.
The only temporary mail site without ads is no longer alive. Although he is in first place in Google and Yandex.
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Developer training.
Servers eat a little there.