How does mailgun work?

Question

Mail server

The question is more about the "materiel" concerns the mailing service.
The question is, how do mail services send out letters and such a large number of letters??

That is, how do they set them up so that they can send millions of letters a day.
I'm not for spam)) But more on work, you need to get some information.

Answer 1

https://sendpulse.com/en/blog/warming-up-new-ip-address

Answer 2

What's special? There are no technical restrictions on mailing - you can send millions. And quickly get into all sorts of spam lists. Do not use? Well your problems...