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Editorial Team
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Asked: 2026-06-05T04:10:37+00:00

I am continously sending mails from different addresses, and I haven’t had any problems

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I am continously sending mails from different addresses, and I haven’t had any problems so far.

Now I am sending a new mail (just ONE email), and in the client.Send(message) line it throws an exception; 

{System.Net.Mail.SmtpException: El buzón de correo no está disponible. La respuesta del servidor fue: 5.7.1 Mail refused, your IP is blacklisted - See http://www.spamhaus.org/query/bl?ip=+186.49.3.153

I have been looking around but have had no luck. I have never sent an email from this address, but if I change the credentials and try sending from another account, I have no problem.

I followed the link, and looked up for the ip address in the message error (186.49.3.153). This link leads to the page where it says that the IP is listed on the Policy Block List (PBL). I read the description, saying that if I am using any normal email software (Outlook, Entourage, etc) then it is simply because I need to turn on “SMTP authentication”.

However, this is not the case since I am sending emails using .NET. Any ideas of what I should do?

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1 Answer

  1. Editorial Team

    Your mail server IP is being blocked (as the website provided will show).

    The webpage explains why you are blacklisted.

    Its also possible if your not on a static IP that you are using an IP that someone else has caused to blacklist.

    For what ever reason you are blocked, there is an option provided to unblocking your IP. Just follow the instructions, and you should be up and running again shortly.

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