High Speed Verifier (HSV) is a high-speed software designed to check e-mail address for existence. HSV is capable of checking thousands of addresses per second. It can easily deal with mailing lists containing tens millions of addresses; moreover, it is with this list size that the program's highest performance can be achieved. HSV detects about 20-30% of invalid addresses in a mailing list, though theoretically it is possible to detect up to 60-70% using a software product. This figure seems relatively small, but actually it might make 10% of a list. Besides, HSV provides for optimal checking mode in terms of time and data traffic. More thorough checking (with which the rest 40% of dead emails could be detected) takes 10 times longer and requires 5 times greater traffic for each address, hence it's not that advisable with huge lists.