The certificate company will send a confirmation email to one of the following five mailboxes:
- admin@domain.com
- administrator@domain.com
- hostmaster@domain.com
- postmaster@domain.com
- webmaster@domain.com
The company will send you a code. You need to create a TXT file with the content of that code, and upload it to the website at the link:
http://tenmien.com/.well-known/pki-validation.txt
Or:
https://tenmien.com/.well-known/pki-validation.txt
The certificate company will send a piece of code for you to put on the website's DNS record. After you update your records on DNS, the company will check and confirm that you own the website.