36 comments found.
its not working all emails Unknown
1. Why does verification show “Unknown”? This status means the target mail server did not clearly confirm whether the mailbox exists. Some major providers — especially Gmail, Outlook, Yahoo, and iCloud — use anti-spam protection policies that hide real verification results during the SMTP handshake.
These servers intentionally return a generic response (such as 250 OK) for both valid and invalid addresses, so no external tool can know the actual mailbox status without sending a real email.
Reasons:
Mailbox verification is disabled on the provider’s SMTP gateway (for privacy and anti-spam reasons). The server always responds with “accept all” behavior (Catch-All or Greylisting). Temporary 4xx responses or connection delays (rate limits, throttling, tarpitting). Recommended actions:
Treat “Unknown” results from Gmail/Outlook as potentially valid — not as invalid. Use the Trust Score and domain reputation data for confidence ranking. Re-check later from a different IP or network if needed. Combine SMTP verification with pattern-based analysis (MX, DNS, SPF/DMARC, disposable domain detection).
hello please i buy this and i dont know hoe to start the app where is the app
on you download file
The port 25 has been enabled and is now listening. In most cases, I get the message “The SMTP service is not available”, but sometimes it replies with “550 Invalid Recipient [smtp-21.iol.local; LIB_520]”.
So does this mean the emails are actually working? Everything has been done with administrator privileges.
Hello, Thank you for your detailed explanation.
The message “550 Invalid Recipient [smtp-21.iol.local; LIB_520]” indicates that your SMTP server is reachable and responding — so technically, the connection and email-sending process are working. However, the recipient address is being rejected by the remote mail server, which means the issue is related to the recipient’s validity or SMTP policy, not the software itself.
The message “SMTP service is not available” usually appears when the remote server temporarily refuses the connection or limits access, which can happen due to security filters, rate limits, or anti-spam rules.
Since port 25 is active and responding, your configuration is correct. You may simply need to verify recipient addresses or try again later with different domains.
If the software doesn’t use a proxy, the IP address will always be banned after 10 or 20 requests.
Thank you for your feedback. Please note that the software itself does not include a built-in proxy feature. The full source code is provided, so you can freely add or extend proxy support if needed.
If you perform a large number of verification requests without using proxies, please make sure to add a reasonable delay between requests. Otherwise, mail servers may temporarily block or limit your IP address due to excessive access frequency — this is a normal anti-abuse mechanism.
To ensure stable verification performance, we recommend:
Using rotating proxies or VPNs;
Setting a proper delay (1–3 seconds) between each request if no proxy is used;
Limiting the number of verifications per batch;
Simulating realistic user access patterns to maintain stability.
The product includes full source code, allowing you to easily integrate third-party proxy APIs or customize delay logic based on your needs.
Thank you for your understanding and support.
The port 25 has been enabled and is now listening. In most cases, I get the message “The SMTP service is not available”, but sometimes it replies with “550 Invalid Recipient [smtp-21.iol.local; LIB_520]”.
So does this mean the emails are actually working? Everything has been done with administrator privileges.
Hello, Thank you for your detailed explanation.
The message “550 Invalid Recipient [smtp-21.iol.local; LIB_520]” indicates that your SMTP server is reachable and responding — so technically, the connection and email-sending process are working. However, the recipient address is being rejected by the remote mail server, which means the issue is related to the recipient’s validity or SMTP policy, not the software itself.
The message “SMTP service is not available” usually appears when the remote server temporarily refuses the connection or limits access, which can happen due to security filters, rate limits, or anti-spam rules.
Since port 25 is active and responding, your configuration is correct. You may simply need to verify recipient addresses or try again later with different domains.
Great work!
thanks
Please, the email verification is not working I tested it with 3 of my vaid emails, and its says invalid. please, what’s going on with the software? Can you help me out
Request from your VPS server provider a dedicated IP then request them to enable Windows SMTP Server through VPS.
Hello, I just bought Email Verifier Pro and try to install it. It ask to install .net .I downloaded .net 9.0 and install it. Unfortunatelly your software don’t work. Why?
Guy Hautot
Request from your VPS server provider a dedicated IP then request them to enable Windows SMTP Server through VPS.
I have a windows server now , installed SMTP Service, allowed all the ports from that server but still getting the same error ” The SMTP Service is not available” I have checked that SMTP service on windows server is running. I have run the visual studio on Admin mode and also tried port 25 and 587 both. Please guide.
hi sir. the problem was way simpler than it looked. It was simply a matter of the ISP blocking port 25. So, check with your ISP!
I have checked this sir!! I am able to telnet on port 25 from the same machine but from the code it is not working.
It was the ISP blocking port 25.or you can try vps.
Request from your VPS server provider a dedicated IP then request them to enable Windows SMTP Server through VPS.
Hi There, I have purchased the software and trying to use it. For all the emails it is giving error “The SMTP Service is not Available”. I have opened the firewall and allowed all the TCP ports for outbound, disabled the antivirus. Please guide.
The line where it gives error is this : if (!tcpClient.ConnectAsync(this.host, this.port).Wait(15000)) { throw new SmtpClientTimeoutException(); }
Request from your VPS server provider a dedicated IP then request them to enable Windows SMTP Server through VPS. @author – this is what you should reply – not ‘SMTP WINDOWS VPS GO FIND’
Any documentation to buy and run on the VPS server? I am running this on my local machine.
Or run on a window server, make sure your smtp service is turned on.
I understand why this has 2.3 stars. People ask question – author answers ‘learn smtp’ – doesn’t include it in his installation – doesn’t provide support. Sad story man, this could be really good and he’s just letting it turn to rubbish.
Free advise for those unable to connect: Request from your VPS server provider a dedicated IP then request them to enable Windows SMTP Server through VPS. @author – this is what you should reply – not ‘SMTP WINDOWS VPS GO FIND’
thanks sir.
Hi There! wanted to know if this tool and code verifies the email existence without sending the email or does it send the actual email?
this don’t send mail.
Hello I bought and try to hard to make this software works but with no success.
Pls agree to refund. I am not satisfied and will not use the software anymore. Too much headache.
Is still working? Any email? Any quantify?
To work on a window server, you need to enable the stmp service.
But how I can configure?? How I need to do on my client?
You can search how to enable stmp service in window server
Have document on your software showing this? How I can do on my client? It’s difficult?
Regarding how to configure the Windows system, this is a Windows system setting issue, you need to solve it yourself
Hello,
With emails like abc@domain that has domain like codecanyon.net or cambridge.org,etc…
So your script can verify it or not?
work on smtp server
Hi brother, I have used this bfore and for anyone reading comments – THIS SOFTWARE DOES WORK. I’ve lost my previous VPS and need to setup again, could I pay you for setup please brother?
you cans search “how to open smtp port”
I don’t know how to use, I don’t know how to put an smtp nor how to activate the port 25 so I want to be reimbursed, I need a video to explain.
hi sir you can run window server
Hi Sir, I bought two apps a few days ago Super Bulk Email Verifications for $59 and (Verify Pro and Fast Google Email Phone Extract Pro for $99). The Extract Pro is working great this Email verification is not working. It is invalid, even working emails. I need this app to work. I even downloaded Visual Studio 11GB b/c the documentation doesn’t tell you the required vs. Also, I downloaded Framework net core, so are you updating the app? or what is the solution? I appreciate any help you can provide.
1.email pro can only work on smtp server. 2. If you need to work on this machine, please make sure that port 25 of your computer is open.
Thanks, I did open and Run the program as administrator, Disable the firewall, and open port 25 on my computer. Can you explain what you mean by saying, “email pro can only work on SMTP server” how do you run on the SMTP server?
Usually, port 25 cannot be enabled on win10, and many users think that the program cannot work. You can open it on the window server, open port 25, and run this program.
I see thank you.
Hi, the import is not opening or recognizing Excel or Microsoft Word document.
it work before and now not working, and i complained , it work not all domains, gamail and yahoo ork and others not
THIS NOT WORKING AGAIN? PLEASE WHAT HAPPENED?
hi sir, please make sure to run on the smtp server
this not working on other mails only on gmail
