The Command Prompt console in Windows 7, 8 and 8.1 lets you check the validity of an email address by pinging it. Once you get the list of MX (Mail Exchange) records for the domain of an email address, you can connect to the domain's mail server and communicate with the email address for verification. You must, however, turn on the Telnet remote access protocol before you can start the process.
Press Windows-R to open the Run box, type optionalfeatures, and then press Enter to open the Windows Features panel. Check the box next to Telnet Client, and then click OK to turn on Telnet. Restart your computer to finalize the changes.
Press Windows-X, and then select Command Prompt to open the Command Prompt console in Windows 8/8.1. On Windows 7, click the Start button, type Command Prompt, and then press Enter.
Type nslookup –type=mx domain.com into the Command Prompt console, replacing domain.com with the domain of the email address that you need to ping. Press Enter to load the list of MX records for the domains, which you can find next to Mail Exchanger. For example, MX records read as gmail-smtp-in.l.google.com for Gmail, mx1.hotmail.com for Hotmail.com and Outlook.com, or mta5.am0.yahoodns.net for Yahoo.com.
Use the Telnet protocol to connect to the domain's mail server. For example, when connecting to Gmail, enter Telnet gmail-smtp-in.l.google.com 25, where you can swap gmail-smtp-in.l.google.com with any of the other Gmail MX records. Press Enter to connect.
Type HELO, and then press Enter to communicate with domain's mail server. Next, type mail from:email@example.com, replacing firstname.lastname@example.org with your email address. Press Enter, and then type rcpt to:email@example.com, replacing firstname.lastname@example.org with the email address that you need to ping.
Press Enter to ping. If the email address exists, you receive an "OK" message. If the email address isn't valid, you get a "Does Not Exist" or "Disabled" message.
Websites such as VerifyEmailAddress.org, Email-Checker.com and Email-Validator.net (links in Resources) let you verify email addresses without you having to input any commands.
To turn off Telnet after pinging an email address, open the Windows Features panel, uncheck Telnet, and then click OK.