Welcome to BulkVerifier, an efficient multi-threaded application for checking e-mail addresses and domain availability. Quickly and easily verifies email addresses, huge domains and clean up your mailing / domain list. A powerful advanced bulk domain and email validation tool.

BulkVerifier v2.2 (New version!) offers you two processing modes fast and deep.

In its fast mode BulkVerifier works extremely fast being able to process mailing lists containing dozens of millions of e-mail addresses at a speed of several thousands addresses per second. This mode does not ensure the highest accuracy of checking/cleaning but is optimal by expended time and traffic and provides quite sufficient results. We recommend the fast processing mode of BulkVerifier as a high-speed tool for sifting obvious rubbish out of large mailing lists containing millions of e-mail addresses.

In its deep mode (default), BulkVerifier works significantly slower but provides much more precise results. Optimal data amount for this mode is 70...100 thousand e-mail addresses. We recommend the deep processing mode of BulkVerifier as a slow but high-quality tool for checking of not very large mailing lists.

General BulkVerifier features

Smart mode

New feature, available from version 2.0. In this mode application will send test message to verify e-mail addresses. Warning! This could be considered as SPAM in some cases.

Incoming file formats

BulkVerifier domain and email verifier tool can process both plain list of e-mail addresses / domains where each line contains one item and files of more complex structure like CSV file where lines represents multi-field records of the same structure (i. e. containing the same fields separated with the same delimiter). For example, you can export a worksheet of an MS Excel file to check availability of e-mail addresses/domains listed there. It’s supposed that one line of an incoming file contains one e-mail address and/or one domain. To specify the format of the incoming file please turn to the Options dialog.

BulkVerifier internal cache

This advanced email verifier stores domain check results in the internal cache. If another e-mail address from the same domain will be found in the same mailing list, Bulk Verifer will not request the DNS server once again but will use the result from the cache. Cache size is limited only by the memory size of your computer. It takes 40 bytes of memory to store the result of one domain check. Thus, it will take 40 MBytes of memory to store the results of check of one million different domains. The time spent to find a previous check result in the cache practically does not depend on the cache size.


The quality of DNS servers list used by BulkVerifier (Options\DNS) also influences deeply the application performance. If Bulk Verifier does not receive a response from a DNS server in a specified period of time (Options\Timeout, in seconds), it makes new attempts using another DNS service from the list each time. If all these attempts failed, the e-mail address is listed as not checked due to the connection timeout. The bigger the list of DNS servers which can be used by E-mail Verifier, the less is the probability that a couple of DNS servers which have operating problems will affect the application’s performance.

Multithread processing

This bulk domain and email verifier is a multi-thread application. You can define up to 600 threads which will be used simultaneously (one thread is used to check one e-mail address/domain from mailing list and determine if domain/e-mails are still valid).

Please note that using the maximal number of threads is not always the best choice. For example, if you use 600 threads, the application checks 600 domains at the same time sending up to 15 000 requests for DNS servers per minute. At that the traffic may amount to 700 kbps. A DNS server’s software may regard this as a hackers attack and block you up.

It is also possible that DNS server can process only a certain limited amount of requests per second from the same address ignoring the rest of requests to ensure other users have enough resources to work with the server. In this case the application productivity will decrease significantly since some addresses will be checked repeatedly because previous attempts to check them were unsuccessful due to timeouts.

Thus, if your network connection is capable to provide the work of more than 50 threads, you should adjust your Bulk Verifier parameters as about one DNS server (Options\DNS) per each ten threads. In this case you can be sure that servers will not fail because of the overload.

Multithread applications work in different ways with different operation systems of Windows family. Windows XP perfectly copes with 600 processing threads; at that the processor load increases insignificantly. Older operation systems (e. g. Windows’98, Windows NT4) are more sensitive to big threads number and even a hundred of threads may lead to a considerable processor load. We recommend you to use Bulk Verifier on computers controlled by Windows XP to reach the application’s maximal performance.