What shall I do to stop the testing of the DNS-servers? I don't want to receive any letters. During domain registration I specified DNS-servers, which don't host the zone.

To stop testing you will be required to:

- log in to "Manage your account";
- choose in the menu "Services. Review and update data → My domains";
- find the necessary service (domain registration);
- in section "DNS servers" choose "Modify";
- click on "Stop testing".