Failure sending mail (using Gmail Service)

Question

User944339287 posted

Hi guys.. i getting this error while trying to send an email via smtp.gmail.com
The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Authentication Required. Learn more at

The following is my code for sending emails out. [e-mail] is a Google business email account.
This web application is parked at www.byebye.com which let system user send an email out.

Anything wrong to my code or setting?

    Public Function SendEmail() As Boolean

        Dim success As Boolean = False

        'Recipient email
        Dim [to] As String = "[e-mail]"
        Dim cc As String = ""
        Dim bcc As String = ""

        'Sender email
        Dim from As String = "[e-mail]"

        'Sender account
        Dim fromName As String = "HELLO WORLD"
        Dim userName As String = "[e-mail]"
        Dim password As String = "fd##4jhAbWQ"

        Dim attachment As Attachment = Nothing

        Dim client As New SmtpClient()
        client.EnableSsl = "True"

        client.Credentials = New System.Net.NetworkCredential(userName, password)
        client.Port = "587"
        client.Host = "smtp.gmail.com"

        Try
            Using mail As New MailMessage()
                mail.From = New MailAddress(from, fromName)
                mail.ReplyTo = New MailAddress("[e-mail]")
                mail.Sender = mail.ReplyTo

                If [to].Contains(";") Then
                    Dim _EmailsTO As String() = [to].Split(";".ToCharArray())
                    For i As Integer = 0 To _EmailsTO.Length - 1
                        mail.[To].Add(New MailAddress(_EmailsTO(i)))
                    Next
                Else
                    If Not [to].Equals(String.Empty) Then
                        mail.[To].Add(New MailAddress([to]))
                    End If
                End If

                mail.Subject = "Testing Mail from Gmail Server"
                mail.SubjectEncoding = System.Text.Encoding.UTF8

                mail.Body = "HELLO WORLD"
                mail.IsBodyHtml = True
                mail.BodyEncoding = System.Text.Encoding.UTF8

                'attachment
                If attachment IsNot Nothing Then
                    mail.Attachments.Add(attachment)
                End If

                client.Send(mail)
                success = True
            End Using

        Catch ex As Exception

        End Try
        ' end try 

        Return success

    End Function

Answer 1

User-939850651 posted

Hi kengkit,

Google may block sign in attempts from some apps or devices that do not use modern security standards. Since these apps and devices are easier to break into, blocking them helps keep your account safer.

For example, some third-party applications such as desktop mail clients ( such as Microsoft Outlook ,Mozilla Thunderbird,etc).

Therefore, you have to enable Less Secure Sign-In (or Less secure app access) in your google account.

After sign into google account, go to ---> https://www.google.com/settings/security/lesssecureapps

You could also refer to this similar case:

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

Best regards,

Xudong Peng