Bad e-mail addresses are sometimes marked as good

eMail Verifier checks every address from a given mailing list, using the same algorithm as ISP mail systems do, allowing you to determine up to 70-80% of "dead" mail addresses. Addresses for email are extracted from a Domain Naming Server (DNS) and eMail Verifier tries to connect with SMTP-servers and simulates the sending of a message (A Domain Naming Server (DNS), or Domain Name System, is what turns an internet name like www.yahoo.com into an internet address, such as 216.109.118.77).

For some addresses, such as AOL, Yahoo, and other non-SMTP mail, you can't verify whether  the address is good or not. You won't know definitively until some bounce. The mail server won't cooperate and as a result addresses will be marked as valid. In fact, a few ISP's mail servers are configured in a way they prevent anybody to find out if an e-mail address is good or not sometimes to protect their customer e-mail addresses from harvester tools. Note that bounces can be easily processed with eMail Bounce Handler, a tool that can scan your mail box, locally or remotely, and create a clean list of bad e-mail addresses. Using both eMail Verifier and eMail Bounce Handler is explained here.

eMail Verifier already offers a list of non-cooperating server in the preferences, 'Rules' panel. You can add more servers to the list. That will speed up the verifying process since no connection will be made to those servers.

Consider eMail Verifier as a tool for tracking bad e-mail addresses instead of validating good ones. It is always a plus to have as few bad email addresses in a list as possible. It would be terrific to be able to detect all those dead email addresses and generates 100% clean lists. Unfortunately that is no longer possible. Anyway it is highly recommended to clean your lists with eMail Verifier since a high bounce rate can flag your message as spam in given systems.