The program works the same way as do providers' mail servers: it issues a DNS request to define recipient's MX (Mail Exchange) server. After that, it imitates the sending of a message. In this process, no actual messages are sent to server - the program analyzes the server's response to the RCPT TO: command, which allows to determine the validity of the address with fine accuracy.

Mail List Validator uses Rules for determining bad e-mail addresses. That allows to achieve very high accuracy of the validation. The program is capable of finding all invalid addresses in a list, is absolutely free from the false trigger instances (where a valid address would be marked as invalid.)

Program's features:

Freeware. Mail List Validator is absolutely free (freeware); it does not require registration and does not have any functionality restrictions!
Quick DNS Validation. The program supports a special validation mode where it only issues a DNS request to resolve MX servers for the e-mail address' domain name. Using this mode, you can quickly find and remove addresses with domain names that no longer exist.
Multi-Threaded Validation. The program can simultaneously validate several dozens or hundreds of e-mail addresses. This allows loading your Internet port to its limit and thus complete the validation at the greatest possible speed.
Validates Large Lists. Mail List Validator does not have hard restrictions on the size of address lists being checked (the only major restriction is the database size must not exceed 4 gigabytes.) Thus, the program can easily validate address lists containing several millions of addresses each.
Allows Setting Custom Validation Rules. Use this function to create groups of addresses that cannot be validated due to the IP address being blocked, problems with HELO domain or other server's specific errors. This actually allows automatically marking addresses differently, depending on MX SMTP servers' responses.
Uses Rules for Validating Addresses. During the validation process, the program compares server's response with the predefined list of typical responses for unavailable addresses. An address is marked as Invalid ONLY IF the server's response matches at least one line of that list. In no other cases an address will be marked as Invalid. Thus, situations where a good address is marked as bad are completely eliminated, and the performance features very good accuracy.
Imports Address Lists from All Data Sources. The program allows importing address lists from plain-text and CSV files, Windows Address Book, and from other data sources via ADO/ODBC.
Powerful Address Search and Removal Functions. The program contains a powerful query builder that allows searching addresses with flexible criterions and saving results to file or discarding them.

The license of this software is Freeware, you can free download and free use this contact management software.