Mail Exchange or MX records verification.
This is where the bulk email verifier flexes its muscle by looking up and analyzing the so-called Mail Exchange or MX records in a domain.
MX records are a type of Domain Name System (DNS) records that define the mail servers that are in charge of accepting emails for a given domain.
If MX records do not exist or are incorrect, the email is classified as invalid.
Disposable email address detection:
It also scans to check whether a given email address is disposable – temporary, like Mailinator or Guerilla Mail for example.
In most cases, temporary emails are created for short-term single-use exposure and are generally labeled substandard for long-term use for marketing purposes.
Catch all detection:
There are some email addresses, pretty many to be frank, which are designed or warbled so that it could receive any type of email aimed at them.