smtp.live.com - mailbox unavailable. The server response was: 5.7.3 requested action aborted; user not authenticated

Question

I have read other answers on the stackoverflow. but none of the solutions work for me.

I'm trying to send email through live.com, but unable to it.

The error message:

mailbox unavailable. The server response was: 5.7.3 requested action aborted;
user not authenticated

The code:

MailMessage mail = new MailMessage();
mail.From = new MailAddress("[email protected]");
mail.To.Add("[email protected]");
mail.Subject = "hello";
mail.Body = "awefkljj kawefl";
mail.IsBodyHtml = false;

SmtpClient smtp = new SmtpClient("smtp.live.com", 587);
smtp.EnableSsl = true;
smtp.Credentials = new NetworkCredential("[email protected]", "password");
smtp.Send(mail);

Are you able to send the email by using above code?

It works before, last year, but it is no more working now.

What had been changed?

Answer 1

I ran into an issue where I was unable to send emails using the smtp.live.com SMTP server from certain hosts -- particulary Azure hosts. In my case, the SMTP attempt was from a host that I had never used to sign-in previously, so the attempt was blocked with the 5.7.3 error:

Mailbox unavailable. The server response was: 5.7.3 requested action aborted; user not authenticated

The solution was to browse to the account settings, locate the SMTP request in its recent activity, and select "This was me":

Answer 2

In my case I was using a gmail account but was telling the service otherwise. I changed:

smtp.Host = "smtp.live.com";

To:

smtp.Host = "smtp.gmail.com";

Which resolved my issue.