The option is allowed in the menu “Verify”/ “Common settings”/ tab “DNS settings”.
DNS determines IP-addresses. It means that it transforms symbol names into IP-addresses.
DNS servers are for resolving the target mail servers that email messages should be delivered to and also stores other types of information, such as the list of mail servers that accept email for a given Internet domain.
DNS protocol settings are defined into this tab.
Use system defaults — if this option is checked, Atomic Mail Verifier will try to load system default DNS settings.
Use specified DNS values — if this option is checked, you are asked to enter user DNS server addresses in “Primary” and “Secondary” fields.
Threads count — specifies the number of threads that work simultaneously while checking domain names. Setting this value to very small number of threads (less than 5) or large number (more than several hundreds depending on your computer performance) may significantly slow down the entire process.
Retries count — specifies the number of retried connections to each DNS server. The recommended setting is 2-3 retries (if the DNS server does not respond after 2-3 retries move on to the next DNS server on the list).
Caching DNS request — is checked for saving DNS requests.