How can you parse emails/names of people all over the internet?

Question

Programming

Recently I became interested in searching and analyzing data using search engines + came across a couple of interesting services that are tied just to this. It became interesting how they work, but he himself did not find anything worthwhile. I hope the power of the Toaster will come to the rescue.
First: https://emailhunter.co/
The essence of the service is approximately the following: you enter the site address, and all emails that are located at this address are returned to you. Judging by the form of issue, in particular by the "sources" tab, the site somehow parses the word that ends with "@domain.com". At first I thought that some kind of Google API was used, but as it turned out, Google has a limit of 10k requests per day. Considering that even an average EmailHunter subscription offers 20k requests, one can assume that this is not a Google API. And now I can't even imagine how they are looking for these emails.
Another service is https://charlieapp.com/.
Service example: https://charlieapp.com/briefings/deCPb-5SlRLXZDibB...
It's about something completely different: it parses Google Calendar and gives you information about the person you're meeting with. For example, a list of his social profiles. networks, blog, where he works, etc. The interesting thing about him is that he can find news about a person and articles about a company. Here, too, it is not very clear how he searches for news and articles.

Answer 1

Spammers let them look for their lotions.

Answer 2

Maybe they are collecting a database of emails that have been hacked/stolen or they have their own bot that roams the internet and collects soaps...