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 and enable less secure apps. So that you will be able to login from all apps.

This Go program successfully sends email from my home computer, but on a virtual server on DigitalOcean receives the following error: panic: 530 5.5.1 Authentication. I got this error for few email address.User Authentication is done from gmail.Error is below The SMTP server requires a secure connection or the client was.

Solution 2 for case 2:(see ) 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.

Korean Drama I Hear Your Voice Sub Indo. 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 and allow access by clicking the continue button. And that's it. Now you will be able to login from any of the computer and by any means of app to your google account.

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): 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'. I'm a google apps for business subscriber and I spend the last couple hours just dealing with this, even after having all the correct settings (smtp, port, enableSSL, etc). Here's what worked for me and the web sites that were throwing the 5.5.1 error when trying to send an email: • Login to your admin.google.com • Click SECURITY.