Gmail Error :The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required

Question

I am using following code to send email. The Code works correctly in my local Machine. But on Production server i am getting the error message

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Answer 1

Its a security issue, Gmail by default prevents access for your e-mail account from custom applications. You can set it up to accept the login from your application.

After Logging in to your e-mail, CLICK HERE

This will take you to the following page

Answer 2

A comment from Tomasz Madeyski is what fixed my problem... he tells that exists a bug on SetDefaultCredential, him says:

"The issue is that in UseDefaultCredentials setter there is this code: this.transport.Credentials = value ? (ICredentialsByHost) CredentialCache.DefaultNetworkCredentials : (ICredentialsByHost) null; which overrides credentials set by Credentials setter. For me it looks like SmtpClient's bug"

if you put smtpClient.UseDefaultCredentials = false after set credentials... this line set to null those credentials...

Answer 3

First, I purchased the domain in GoDaddy, and when I clicked this link https://www.google.com/settings/security/lesssecureapps I didn't have the option, it show this message "The domain administrator manages these settings", so I go to the Admin Console https://admin.google.com/

There is this option

Then appears the option that I needed in

Answer 4

I used all of the above mentioned solutions but it finally worked only after i enabled IMAP Access from Gmail settings Link to Enable IMAP Access in gmail settings

Of course, the points in the other solutions were required too.

Answer 5

After spending a couple of hours today trying every solution here, I was still unable to get past this exact error. I have used gmail many times in this way so I knew it was something dumb, but nothing I did fixed the problem. I finally stumbled across the solution in my case so thought I would share.

First, most of the answers above are also required, but in my case, it was a simple matter of ordering of the code while creating the SmtpClient class.

In this first code snippet below, notice where the Credentials = creds line is located. This implementation will generate the error referenced in this question even if you have everything else set up properly.

System.Net.Mail.SmtpClient client = new System.Net.Mail.SmtpClient
{
    Host = Emailer.Host,
    Port = Emailer.Port,
    Credentials = creds,
    EnableSsl = Emailer.RequireSSL,
    UseDefaultCredentials = false,
    DeliveryMethod = System.Net.Mail.SmtpDeliveryMethod.Network
}

However, if you move the Credentials setter call to the bottom, the email will be sent without error. I made no changes to the surrounding code...ie...the username/password, etc. Clearly, either the EnableSSL, UseDefaultCredentials, or the DeliveryMethod is dependent on the Credentials being set first... I didn't test all to figure out which one it was though.

System.Net.Mail.SmtpClient client = new System.Net.Mail.SmtpClient
{
    Host = Emailer.Host,
    Port = Emailer.Port,
    EnableSsl = Emailer.RequireSSL,
    UseDefaultCredentials = false,
    DeliveryMethod = System.Net.Mail.SmtpDeliveryMethod.Network,
    Credentials = creds
}

Hope this helps save someone else some headaches in the future.

Answer 6

I had the same problem for an application deployed to Microsoft Azure.

SmtpException: The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required.

First I approved all unknown devices (some ip-addresses originating from Ireland) on the following page (signed in as the gmail user): https://security.google.com/settings/u/1/security/secureaccount

I used the following settings for the client:

var client = new SmtpClient("smtp.gmail.com");
client.Port = 587;
client.EnableSsl = true;
client.UseDefaultCredentials = false;
client.Credentials = new NetworkCredential("my_user_name@gmail.com", "my_password"); 

It started working only after I set the following property on the smtp-client:

client.TargetName = "STARTTLS/smtp.gmail.com";