Pay for gmail, that's it. You can pay for hotmail as well. If you are curious how safe are emails then spin up a VPS for a few bucks in your currency. Now sit and watch as emails come in and go out.
You have clearly stated in your footnote that if anything goes wrong then the given numbers can go down. To be honest, that's what happens all the time. Developers do something wrong and number of requests just drop down to the floor.
Only static websites are the one which handle large amount of requests at low cost. Web hosting providers don't make money out of those clients, so they run shared plans.
Donations, community support, and patreon like subscription model helps OpenDesktop to sustain. I know there are not free lunches, but this is how it looks like. One must pay for someone else to keep the flow running.
Those who are not, must be feeling unworthy now.
He is a professional "book summarizer" too.
I feel like a professional commentator now.