How to check an existing MX record? How to find out that the mail does not exist? How to check that the domain does not exist?

Question

Domain Name System

I want to try to do verification from one-time emails. The question arose - how to programmatically check MX records on a specific domain?
How to find out that the mail does not exist? (the option with a link to the mail is obvious. do not offer)
How to find out that the domain does not exist most effectively? Well, i.e. do not wait a few minutes for an answer, but immediately find out the status.

Answer 1

dig - check mx, whois - check domain.
You can send mail from any mailbox, even non-existent, the problem is that a normally configured mail server will reject this letter because it will not pass spf, dkim and dmarc checks.

Answer 2

How to find out that the mail does not exist?

No way. The mailer is not required to comply with postal standards, he is recommended to do so. But due to the fact that such people "checked" divorced like Prussians in an drunkard's apartment, very often letters to non-existent users (as well as to those fired, etc.) go to a special user. It can be a regular user whose mailbox is cleaned daily or /dev/null. The postman received the letter. And gave it to /dev/null. From your point of view - there is a box. Actually, it doesn't exist :)