VB .net Sending Email System using yahoo or google failed to send

Question

Good Day, I have a system for sending email using VB .Net since 2012. But last week this program failed to send email. Is there an update from microsoft related on this? I try both yahoo or gmail server but still not working.

This is my Code:

Dim Smtp_Server As New SmtpClient
Dim e_mail As New MailMessage()
Smtp_Server.UseDefaultCredentials = False
Smtp_Server.Credentials = New Net.NetworkCredential(TextBox_SenderEADD.Text, TextBox_Password.Text)
'Smtp_Server.Port = 587
Smtp_Server.Port = 465
Smtp_Server.EnableSsl = True
'Smtp_Server.Host = "smtp.mail.yahoo.com"
Smtp_Server.Host = "smtp.gmail.com"

e_mail = New MailMessage()
e_mail.From = New MailAddress(TextBox_SenderEADD.Text)
e_mail.To.Add(TextBox_Eadd.Text)
If MailSubject = "Senttoall" Then
e_mail.Subject = TextBox_sendtoallsubject.Text
Else
e_mail.Subject = "RCDC Billing Statement for " & Format(DateTimePicker1.Value, "MMMM yyyy") & ""
End If
e_mail.IsBodyHtml = False
e_mail.Body = TextBox_Message.Text
Smtp_Server.Send(e_mail)

Answer 1

Hi @Ritchie Liz ,

Gmail will prevent access for your e-mail account from custom applications. You need to turn on "Allow less secure apps".
Also see: Gmail Error :The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required
Hope it could be helpful.

Best Regards,
Xingyu Zhao
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Answer 2

I just tested a similar code with gmail (Port = 587) and it worked after I updated this parameter :

lesssecureapps

Answer 3

Hello,

If all worked on Yahoo and GMail before then there may be something blocking locally e.g. Windows Defender or a anti-virus application. You can try using SendCompleted event of the SmtpClient object, in the code below on error the error message is written to the IDE, either immediate or output window depending on how you have things setup. One unknown is how MailSubject is used.

Mail code is in a class as this a) keeps form code clean b) is now reusable. The event MessageSendCompleted has a local variable mailMessage which is not used yet if needed provides access to the MailMessage in the SendSingleMessage method.

Imports System.ComponentModel
Imports System.Net
Imports System.Net.Mail

Public Class MailOperations

    Public Shared MailSubject As String

    Public Shared Async Sub SendSingleMessage(
       userName As String,
       password As String,
       message As String,
       fromAddress As String,
       tooAddress As String,
       subject As String,
       billDate As DateTime)

        Dim Smtp_Server = New SmtpClient("", 0)
        Dim e_mail As New MailMessage()
        Smtp_Server.UseDefaultCredentials = False
        Smtp_Server.Credentials = New NetworkCredential(userName, password)
        'Smtp_Server.Port = 587
        Smtp_Server.Port = 465
        Smtp_Server.EnableSsl = True
        'Smtp_Server.Host = "smtp.mail.yahoo.com"
        Smtp_Server.Host = "smtp.gmail.com"
        e_mail = New MailMessage()
        e_mail.From = New MailAddress(fromAddress)
        e_mail.To.Add(tooAddress)

        If MailSubject = "Senttoall" Then
            e_mail.Subject = subject
        Else
            e_mail.Subject = $"RCDC Billing Statement for {billDate.ToString("MMMM yyyy")}"
        End If

        e_mail.IsBodyHtml = False
        e_mail.Body = message

        AddHandler Smtp_Server.SendCompleted, AddressOf MessageSendCompleted

        Dim token = New Object

        Await Task.Run(
            Sub()

                Task.Delay(1)
                Smtp_Server.SendAsync(e_mail, token)

            End Sub)

    End Sub

    Private Shared Sub MessageSendCompleted(sender As Object, eventArguments As AsyncCompletedEventArgs)

        Dim tempVar As Boolean = TypeOf eventArguments.UserState Is MailMessage

        Dim mailMessage As MailMessage = If(tempVar, CType(eventArguments.UserState, MailMessage), Nothing)

        If eventArguments.Error IsNot Nothing Then
            If TypeOf eventArguments.Error Is SmtpException Then
                Debug.WriteLine($"Smtp error: {eventArguments.Error.Message}")
            Else
                Debug.WriteLine($"General error: {eventArguments.Error.Message}")
            End If
        End If
    End Sub
End Class

Form code

Public Class Form1
    Private Sub SendButton_Click(sender As Object, e As EventArgs) Handles SendButton.Click

        MailOperations.MailSubject = ""

        MailOperations.SendSingleMessage(
            TextBox_SenderEADD.Text,
            TextBox_Password.Text,
            TextBox_Message.Text,
            TextBox_SenderEADD.Text,
            TextBox_Eadd.Text, TextBox_sendtoallsubject.Text,
            DateTimePicker1.Value)

    End Sub
End Class

Answer 4

I try to catch the message error. This was the error appeared during sending email using Smtp_Server.Port = 587

Answer 5

Thanks. I turn on "Allow less secure apps". It works now.