Check Port 25

    Atomic Mail Verifier needs internet and simulation sending a letter to address in order to verify all email addresses. This occurs over the port 25, which is required for SMTP-protocol and is sometimes closed by ISPs.

    Atomic Email Verifier provides three specific modes for checking addresses:

    • Direct connection
    • Web script
    • Proxy connection

    Each of these verification modes has own specifications and purposes. If your ISP has blocked port 25 and the direct connection brings no result, it is recommended to use web script to check email addresses. You can read the detailed instruction about activating and using web scripts for the verification at our website.


    How to check the SMTP connection?

    Click on «Start» - «Run». Then type "cmd" in the "Open:" field and click «OK».



    A new black window will open. To test port 25 use the command:
    «telnet_Your mail server address in format mail.example.com_25».



    If access is successful, you will see the following message.



    If you see «Could not open connection» then your port 25 is closed.

    If you use Windows 7,8,10, you first need to enable telnet: «Start» - «Control Panel» «Programs and Components» - «Turn Windows features on or off». Put a checkmark next to Telnet Client then click «OK».



    What should you do if port 25 is closed?

    1. If the ISP doesn’t block port 25, but Atomic Mail Verifier says that it’s closed, your antivirus program has blocked the program. Turn it off for a while and repeat the procedure again. You can also add Atomic Mail Verifier exception into your antivirus. Following the link below you can learn how to go this:
      Eset NOD32 Smart Security:
      Kaspersky Internet Security:
    2. Ask your ISP to open port 25. If your request is denied, find another provider.
    3. Look for a Wi-fi where port 25 is opened. Wi-fi is available by another ISP and it’s likely that port 25 will be opened.