[Solved] - SMTP Server Secure Connection and Authentication 5.5.1 Required Error | The SMTP Server Requires a Secure Connection or the Client was not authenticated


In previous article I explained How to Send Multiple Emails by Using Gmail Account. Now i show Resolve a SMTP Server Secure Connection and Authentication 5.5.1 Required Error | The SMTP Server Requires a Secure Connection or the Client was not authenticated and How to Send User Confirmation Email after Registration in ASP.NET by using C# Coding.
The SMTP Server Requires a Secure Connection or the Client was not authenticated | The Server Response was 5.5.1 Authentication Required.
  • Please Confirm that you have set SMTP Authentication correctly in your code or not.
  • If there is no problem with your SMTP connection in Codeing, but you still got the message mentioned above, it should because Gmail blocked the authentication from our server as it detected that it is the first time you login to your Gmail account from another Country or Location. You will need to login to gmail security center to approve the authntication. Once you approved it , please wait a few minutes then check afterr registration its sending email from the codeing. Here are the steps to approve the "Access for less Secure Apps from Gmail Security Center.

    Follow this Step


    1. go to Gmail Security Center via this link below or google search for "gmail secrity" and login with your gmail account.
    2. Google Security Center for Email
    3. Click on Access for Less Secure Apps :
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