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

When you try to send mail from code and you find the error "The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required", than the error might occur due to following cases.

case 1: when the password is wrong

case 2: when you try to login from some App

case 3: when you try to login from the domain other than your time zone/domain/computer (This is the case in most of scenarios when sending mail from code)

There is a solution for each

solution for case 1: Enter the correct password.

solution 1 for case 2: go to security settings at the followig link https://www.google.com/settings/security/lesssecureapps and enable less secure apps . So that you will be able to login from all apps.

solution 2 for case 2:(see https://stackoverflow.com/a/9572958/52277) enable two-factor authentication (aka two-step verification) , and then generate an application-specific password. Use that newly generated password to authenticate via SMTP.

solution 1 for case 3: (This might be helpful) you need to review the activity. but reviewing the activity will not be helpful due to latest security standards the link will not be useful. So try the below case.

solution 2 for case 3: If you have hosted your code somewhere on production server and if you have access to the production server, than take remote desktop connection to the production server and try to login once from the browser of the production server. This will add excpetioon for login to google and you will be allowed to login from code.

But what if you don't have access to the production server. try the solution 3

solution 3 for case 3: You have to enable login from other timezone / ip for your google account.

to do this follow the link https://g.co/allowaccess and allow access by clicking the continue button.

And that's it. Here you go. Now you will be able to login from any of the computer and by any means of app to your google account.

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This generally happens when you try login from different time zone or IP Address Computer. Your production server and the mail id you have used both are in different time zone. Choose either of these two solutions:

1) Log in to production server via remote access, and sign in to gmail once with your credentials. They will ask for the confirmation, confirm it and log out.

Or 2) log in gmail to your local computer, Follow this Link and choose review this activity and take proper actions.

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UPDATE 2022

This method no longer works

https://i.stack.imgur.com/SZwTm.jpg

ORIGINAL ANSWER

It is 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

https://i.stack.imgur.com/6C0rU.jpg

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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.

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Hi I had the same issue,

what I've done to solve it. is to turn on the less secure app. after connecting to my gmail account. I entered this link: https://www.google.com/settings/security/lesssecureapps

Then I turn on the secure app and, and the it worked. it has been said also above

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I have a previously-working code that throws this error now. No issue on password. No need to convert message to base64 either. Turns out, i need to do the following:

Turn off 2-factor authentication Set "Allow less secure apps" to ON Login to your gmail account from production server Go here as well to approve the login activity Run your app in production server

Working code

    public static void SendEmail(string emailTo, string subject, string body)
    {
        var client = new SmtpClient("smtp.gmail.com", 587)
        {
            Credentials = new NetworkCredential("youremail@gmail.com", "secretpassword"),
            EnableSsl = true
        };

        client.Send("youremail@gmail.com", emailTo, subject, body);
    }

https://i.stack.imgur.com/cdoNO.png

https://i.stack.imgur.com/wxBTc.png

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Just follow the step in the google email and enable less secure apps.

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I have faced the same problem. It happens when you turn on 2 Step Verification (MFA). Just Turn off 2 Step Verification and your problem should be solved.

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Below is my code.I also had the same error but the problem was that i gave my password wrong.The below code will work perfectly..try it

            MailMessage mail = new MailMessage();
            SmtpClient SmtpServer = new SmtpClient("smtp.gmail.com");             
            mail.From = new MailAddress("fromaddress@gmail.com");
            mail.To.Add("toaddress1@gmail.com");
            mail.To.Add("toaddress2@gmail.com");
            mail.Subject = "Password Recovery ";
            mail.Body += " <html>";
            mail.Body += "<body>";
            mail.Body += "<table>";
            mail.Body += "<tr>";
            mail.Body += "<td>User Name : </td><td> HAi </td>";
            mail.Body += "</tr>";

            mail.Body += "<tr>";
            mail.Body += "<td>Password : </td><td>aaaaaaaaaa</td>";
            mail.Body += "</tr>";
            mail.Body += "</table>";
            mail.Body += "</body>";
            mail.Body += "</html>";
            mail.IsBodyHtml = true;
            SmtpServer.Port = 587;
            SmtpServer.Credentials = new System.Net.NetworkCredential("sendfrommailaddress.com", "password");
            SmtpServer.EnableSsl = true;
            SmtpServer.Send(mail);

You can refer it in my blog

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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";

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After 30th may 2022 Gmail changed it's policy for external apps which using google SMTP for send e-mail For details. Solition is login google account that you want to send e-mail, enable google two step verification and create a password for external app. For details

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Gmail/Google has recently removed (from May 2022) Less Secure app access. This is what they says:

To help keep your account secure, from May 30, 2022, Google no longer supports the use of third-party apps or devices which ask you to sign in to your Google Account using only your username and password.

Now any emailer having direct SMTP email sending will throw error "535-5.7.8 Username and Password not accepted". This is because now Google is asking for app specific password and the email account password isn't app password so they show username/password not accepted.

You need to create and use App specific password. An app password works like an alternate password for your account. It can only be used by the applications you share it with, so it’s more secure than sharing your primary password.

To create app specific password:

Enable 2 Factor Authentication. Go to Account settings of Gmail and select App Passwords. Name it whatever you want and create the password. Use this new 16 digit password along with gmail email for SMTP (At the place of password use this 16 digit password)

Enjoy sending emails..!!

https://i.stack.imgur.com/KkpiS.png

https://i.stack.imgur.com/fM1Es.png

https://i.stack.imgur.com/7qFdt.png

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What worked for me was to activate the option for less secure apps (I am using VB.NET)

Public Shared Sub enviaDB(ByRef body As String, ByRef file_location As String)
        Dim mail As New MailMessage()
        Dim SmtpServer As New SmtpClient("smtp.gmail.com")
        mail.From = New MailAddress("from@gmail.com")
        mail.[To].Add("to@gmail.com")
        mail.Subject = "subject"
        mail.Body = body
        Dim attachment As System.Net.Mail.Attachment
        attachment = New System.Net.Mail.Attachment(file_location)
        mail.Attachments.Add(attachment)
        SmtpServer.Port = 587
        SmtpServer.Credentials = New System.Net.NetworkCredential("user", "password")
        SmtpServer.EnableSsl = True
        SmtpServer.Send(mail)
    End Sub

So log in to your account and then go to google.com/settings/security/lesssecureapps

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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...

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NOVEMBER 2018, have tried everything above with no success.

Below is the solution that worked finally. Unfortunately it's not using SSL, but it works!!!

var fromAddress = new MailAddress(asd@asd.com, "From Name");
var toAddress = new MailAddress("tosend@asd.com", "To Name");

const string subject = "Subject";
const string body = "Body";

var smtp = new SmtpClient
{
    Host = "aspmx.l.google.com",
    Port = 25,
    EnableSsl = false
};
using (var message = new MailMessage(fromAddress, toAddress)
{
    Subject = subject,
    Body = body
})
{
    smtp.Send(message);
}

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So as others have stated correctly, since May 30 google no longer supports the use of third-party apps accessing the account.

https://i.stack.imgur.com/RVB2o.png

https://i.stack.imgur.com/sKZac.png

https://i.stack.imgur.com/Hzrx2.png

I then replaced the generated password, with the one i was using to access my account. In other words one needs to remove the gmail account password(the one we use to login to our gmail) with this new app-password and the functionality was back online!

I hope this helps someone:-)

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I tried all of the suggestions found here, from enabling less secure apps, to trying port 587... nothing worked. Finally I just commented out the line UseDefaultCredentials = false. Everything worked if I didn't touch that boolean.

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You might need to create/generate a specific APP password from gmail. you app or script will then use this new password instead of your regular password. Your regular password will still work fine for you.

That is what did it for me. I still used the same email account but had to generate a new app specific password.

https://support.google.com/accounts/answer/185833?hl=en

https://i.stack.imgur.com/H3vMQ.png

Basically you can do it here: https://security.google.com/settings/security/apppasswords

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dont put break-point before await smtp.SendMailAsync(mail);

:)

when it waits with a break point giving this error when i remove break point it has worked

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I have really looked at a lot of ideas, the only solution was this way (works with different email Providers):

            try
        {
            ViewProgressbar("Try to connect mail-server...", progressBar1.Value = 20);
            string host = dsProvider.Rows[y]["POP_hostOut"].ToString();
            int port = int.Parse(dsProvider.Rows[y]["POP_portOut"].ToString());  //587
            string[] email = von1.Split('@');
            string userName = (dsProvider.Rows[y]["login"].ToString() == "email[0]@email[1]")? email[0]+"@"+email[1] : email[0];
            string password = layer.getUserPassword(listSender.SelectedValue.ToString());
            SmtpClient client = new SmtpClient(host, port);
            client.DeliveryMethod = SmtpDeliveryMethod.Network;
            client.UseDefaultCredentials = false;
            //A idea from MSDN but it not works. You got "The server response was: 5.5.1 Authentication Required."
            //System.Net.NetworkCredential myCreds = new System.Net.NetworkCredential(userName, password, host);
            //System.Net.CredentialCache cache = new System.Net.CredentialCache();
            //cache.Add(host, port, "NTLM", myCreds);
            ///cache.GetCredential(host, port, "NTLM");   //NTLM
            client.Credentials = new System.Net.NetworkCredential(userName, password);
            client.Host = host;
            client.Port = port;
            client.EnableSsl = true;
            client.Send(message);
            ViewProgressbar();
        }
        catch (SmtpException ex)...

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try changing the host, this is the new one, I got this configuring mozilla thunderbird

Host = "smtp.googlemail.com"

that work for me

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