System.Net.Mail.SmtpException SMTP服务器需要安全连接，或者客户端未通过身份验证

Question

I am trying to send SMTP email from my vb.net form application. When applying this code, I get the error below. What am I doing wrong?

Code:

Imports System.Net.Mail

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Try
            Dim SmtpServer As New SmtpClient()
            Dim mail As New MailMessage()
            SmtpServer.Credentials = New  _
            Net.NetworkCredential("myemail@gmail.com", "mypassword")
            SmtpServer.Port = 587
            SmtpServer.Host = "smtp.gmail.com"
            mail = New MailMessage()
            mail.From = New MailAddress("myemail@gmail.com")
            mail.To.Add("sendto@hotmail.co.uk")
            mail.Subject = "Test Mail"
            mail.Body = "This is for testing SMTP mail from GMAIL"
            SmtpServer.Send(mail)
            MsgBox("mail send")
        Catch ex As Exception
            MsgBox(ex.ToString)
        End Try
    End Sub
End Class

Error:

System.Net.Mail.SmtpException: The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Must issue a STARTTLS command first

Answer 1

1. Check if the login and password are correct;
2. Use SmtpServer.EnableSsl = true;
3. Gmail has disabled access using credentials (user and password) by default, you need go to this page: https://www.google.com/settings/security/lesssecureapps and "Enable Less Secure Apps", this means: "Enable login by apps using user and password". More details here: https://support.google.com/accounts/answer/6010255

Answer 2

See if this helps; Add

SmtpServer.EnableSSL= true

Answer 3

I know this was last year but I thought I should publish the answer as five minutes ago I had the same issue.

Basically your log in credentials are incorrect and need changing.

Also thanks for the previous answer has that piece of code allows me to send emails over SSL encryption (I Hope LOL).