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

cgmailnetsmtp

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

var fromAddress = new MailAddress("mymailid@gmail.com");
var fromPassword = "xxxxxx";
var toAddress = new MailAddress("yourmailid@yourdoamain.com");

string subject = "subject";
string body = "body";

System.Net.Mail.SmtpClient smtp = new System.Net.Mail.SmtpClient
{
    Host = "smtp.gmail.com",
    Port = 587,
    EnableSsl = true,
    DeliveryMethod = System.Net.Mail.SmtpDeliveryMethod.Network,
    UseDefaultCredentials = false,
    Credentials = new NetworkCredential(fromAddress.Address, fromPassword)       
};

using (var message = new MailMessage(fromAddress, toAddress)
{
    Subject = subject,
    Body = body
})

smtp.Send(message);

And on my Gmail A/c I have received the following email after i ran the code from production server

Hi ,

Someone recently used your password to try to sign in to your Google
Account mymailid@gmail.com. This person was using an application such
as an email, client or mobile device.

We prevented the sign-in attempt in case this was a hijacker trying to
access your account. Please review the details of the sign-in attempt:

Friday, 3 January 2014 13:56:08 o'clock UTC IP Address: xxx.xx.xx.xxx
(abcd.net.) Location: Philadelphia PA, Philadelphia, PA, USA

If you do not recognise this sign-in attempt, someone else might be
trying to access your account. You should sign in to your account and
reset your password immediately.

Reset password

If this was you and you are having trouble accessing your account,
complete the troubleshooting steps listed at
http://support.google.com/mail?p=client_login

Yours sincerely, The Google Accounts team

Best Answer

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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