'-----
  Private Sub ButtonSendCDO_Click(sender As Object, e As EventArgs) Handles ButtonSendCDO.Click
    Dim str_err As String = vbNullString
    If SendMailMessage("sender@gmail.com", "Отправитель", "Получатель<recip@bk.ru>;", _
     , , _
     "Тема сообщения", "Текст сообщения", True, _
     IO.Path.Combine(Application.StartupPath, "readme.txt"), _
     "smtp.gmail.com", 465, True, "sender@gmail.com", "password", True, True, str_err) Then
      MsgBox("Test mail was sent successfully!", vbInformation + vbOKOnly, "Email was sent")
    Else
      MsgBox("Sending mail...Failed." & vbCrLf & str_err, _
       vbCritical + vbOKOnly, "Sending mail failed.")
    End If
  End Sub

  Private Sub ButtonSendNetMail_Click(sender As Object, e As EventArgs) Handles ButtonSendNetMail.Click
    Dim str_err As String = vbNullString
    If SendMailMessage("sender@gmail.com", "От меня, привет", _
     "recip@bk.ru;Вася<recip@mtu-net.ru>;", _
     "", , "Тема письма", "Письмо по-русски...", True, IO.Path.Combine(Application.StartupPath, "readme.txt"), _
     "smtp.gmail.com", 587, True, "sender@gmail.com", "password", True, False, str_err) Then
      MsgBox("Test mail was sent successfully!", vbInformation + vbOKOnly, "Email was sent")
    Else
      MsgBox("Sending mail...Failed." & vbCrLf & str_err, _
       vbCritical + vbOKOnly, "Sending mail failed.")
    End If
'-----

Imports System.Net.Mail

Module m_SendMail

  Public Function SendMailMessage(Optional ByVal m_msg_FromAddress As String = vbNullString,
                                  Optional ByVal m_msg_FromDisplayName As String = vbNullString,
                                  Optional ByVal m_msg_To As String = vbNullString,
                                  Optional ByVal m_msg_Cc As String = vbNullString,
                                  Optional ByVal m_msg_Bcc As String = vbNullString,
                                  Optional ByVal m_msg_Subject As String = vbNullString,
                                  Optional ByVal m_msg_TextBody As String = vbNullString,
                                  Optional ByVal m_msg_UseUTF8 As Boolean = True,
                                  Optional ByVal m_msg_Attachments As String = vbNullString,
                                  Optional ByVal m_smtp_Host As String = vbNullString,
                                  Optional ByVal m_smtp_Port As Integer = 25,
                                  Optional ByVal m_smtp_UseAuth As Boolean = False,
                                  Optional ByVal m_smtp_UserName As String = vbNullString,
                                  Optional ByVal m_smtp_Password As String = vbNullString,
                                  Optional ByVal m_smtp_UseSSL As Boolean = False,
                                  Optional ByVal m_smtp_UseCDO As Boolean = False,
                                  Optional ByRef str_error As String = vbNullString
                                  ) As Boolean
    ' m_msg_To,m_msg_Cc,m_msg_Bcc -
    ' - в формате "[recipient1<]recipient1@server1.com[>][;[recipient2<]recipient2@server2.com[>][;...]]"
    '(!)теоретически ';' допустимо в DisplayName
    ' m_msg_Attachments -в формате attach1[;attach2[;...]] (!)теоретически ';' допустимо в path
    ' AddLogCDO -полъзовательская ф-ция, которая выводит дебаг напр. в файл - может быть пустая
    SendMailMessage = False

    If m_smtp_UseCDO Then 'CDO.Message
      Try
        AddLogCDO("-------------------------")
        AddLogCDO(Now.ToString & Chr(9) & "Starting sending mail using CDO.Message")
        Dim o_Mess As Object = CreateObject("CDO.Message")
        AddLogCDO(Now.ToString & Chr(9) & "Creating CDO.Message object...Done")
        Dim v_Conf As String = "http://schemas.microsoft.com/cdo/configuration/"
        With o_Mess
          '===(В-1)код необходим для добавления utf-8 в Subject(если .AddAttachment стоит до .TextBodyPart.Charset)===
          If m_msg_UseUTF8 Then .BodyPart.Charset = "utf-8"
          '===(В-1)код необходим для добавления utf-8 в Subject(если .AddAttachment стоит до .TextBodyPart.Charset)===
          If (Strings.Len(m_msg_FromAddress) > 0) AndAlso (Strings.Len(m_msg_FromDisplayName) > 0) Then
            .From = m_msg_FromDisplayName & "<" & m_msg_FromAddress & ">"
          ElseIf Strings.Len(m_msg_FromAddress) > 0 Then
            .From = m_msg_FromAddress
          End If
          If Strings.Len(m_msg_To) > 0 Then .To = m_msg_To
          If Strings.Len(m_msg_Cc) > 0 Then .CC = m_msg_Cc
          If Strings.Len(m_msg_Bcc) > 0 Then .BCC = m_msg_Bcc
          If Strings.Len(m_msg_Subject) > 0 Then .Subject = m_msg_Subject
          .TextBody = m_msg_TextBody
          AddLogCDO(Chr(9) & Chr(9) & "From:" & .From.ToString & vbCrLf & _
           Chr(9) & Chr(9) & "To:" & .To.ToString)
          If Strings.Len(.CC.ToString) > 0 Then AddLogCDO(Chr(9) & Chr(9) & "CC:" & .CC.ToString)
          If Strings.Len(.BCC.ToString) > 0 Then AddLogCDO(Chr(9) & Chr(9) & "BCC:" & .BCC.ToString)
          AddLogCDO(Chr(9) & Chr(9) & "Subject:" & .Subject.ToString)
          If m_msg_UseUTF8 Then
            .TextBodyPart.Charset = "utf-8"
            AddLogCDO(Chr(9) & Chr(9) & "Encoding:" & .TextBodyPart.Charset.ToString)
          End If
          If Strings.Len(m_msg_Attachments) > 0 Then
            For i As Integer = 0 To ChNum(m_msg_Attachments, ";")
              Dim attach As String = Split(m_msg_Attachments, ";")(i)
              .AddAttachment(attach)
              AddLogCDO(Chr(9) & Chr(9) & "Attachment:" & attach)
            Next
          End If
          AddLogCDO(Now.ToString & Chr(9) & "Configuring SMTP")
          With .Configuration.Fields
            .item(v_Conf & "sendusing") = 2
            AddLogCDO(Chr(9) & Chr(9) & "smtpserver=" & m_smtp_Host)
            If Strings.Len(m_smtp_Host) > 0 Then .item(v_Conf & "smtpserver") = m_smtp_Host
            AddLogCDO(Chr(9) & Chr(9) & "smtpserverport=" & m_smtp_Port.ToString)
            .item(v_Conf & "smtpserverport") = m_smtp_Port
            If m_smtp_UseAuth And (Strings.Len(m_smtp_UserName) > 0) And (Strings.Len(m_smtp_Password) > 0) Then
              AddLogCDO(Chr(9) & Chr(9) & "smtpauthenticate=1;sendusername=" & m_smtp_UserName & _
               ";sendpassword=" & StrDup(Strings.Len(Trim(m_smtp_Password)), "*"))
              .item(v_Conf & "smtpauthenticate") = 1 '1 - использовать
              .item(v_Conf & "sendusername") = m_smtp_UserName
              .item(v_Conf & "sendpassword") = m_smtp_Password
            Else
              AddLogCDO(Chr(9) & Chr(9) & "smtpauthenticate=0")
              .item(v_Conf & "smtpauthenticate") = 0 '0 - не использовать
            End If
            If m_smtp_UseSSL Then
              AddLogCDO(Chr(9) & Chr(9) & "smtpusessl=True")
              .item(v_Conf & "smtpusessl") = True 'использовать SSL
            Else
              AddLogCDO(Chr(9) & Chr(9) & "smtpusessl=False")
              .item(v_Conf & "smtpusessl") = False
            End If
            AddLogCDO(Chr(9) & Chr(9) & "smtpconnectiontimeout=60")
            .item(v_Conf & "smtpconnectiontimeout") = 60 'пока считаем что 60, потом м.б. добавим параметр
            .Update()
            AddLogCDO(Now.ToString & Chr(9) & "Configuring SMTP...Done")
          End With
          AddLogCDO(Now.ToString & Chr(9) & "Sending mail")
          .Send()
        End With
        AddLogCDO(Now.ToString & Chr(9) & "Sending mail...Done")
        AddLogCDO("-------------------------")
        Return True
      Catch
        str_error = "Error code: " & Err.Number & " (" & Err.Description & ")"
        AddLogCDO(Now.ToString & Chr(9) & "Sending mail...Failed. " & str_error)
        AddLogCDO("-------------------------")
      End Try
    Else 'System.Net.Mail
      Try
        AddLogCDO("-------------------------")
        AddLogCDO(Now.ToString & Chr(9) & "Starting sending mail using System.Net.Mail")
        Dim message As New MailMessage()
        With message
          AddLogCDO(Now.ToString & Chr(9) & "Creating System.Net.Mail.MailMessage object...Done")
          If (Strings.Len(m_msg_FromAddress) > 0) AndAlso (Strings.Len(m_msg_FromDisplayName) > 0) Then
            If m_msg_UseUTF8 Then
              AddLogCDO(Chr(9) & Chr(9) & "From:" & m_msg_FromDisplayName & "<" & m_msg_FromAddress & ">")
              .From = New MailAddress(m_msg_FromAddress, m_msg_FromDisplayName, System.Text.Encoding.UTF8)
            Else
              AddLogCDO(Chr(9) & Chr(9) & "From:" & m_msg_FromDisplayName & "<" & m_msg_FromAddress & ">")
              .From = New MailAddress(m_msg_FromAddress, m_msg_FromDisplayName)
            End If
          ElseIf Strings.Len(m_msg_FromAddress) > 0 Then
            AddLogCDO(Chr(9) & Chr(9) & "From:" & m_msg_FromAddress)
            .From = New MailAddress(m_msg_FromAddress)
          Else
            AddLogCDO(Chr(9) & Chr(9) & "From:")
          End If
          AddLogCDO(Chr(9) & Chr(9) & "To:" & m_msg_To)
          If Strings.Len(m_msg_To) > 0 Then
            Dim [to_all] As String = m_msg_To
            For i As Integer = 0 To ChNum([to_all], ";")
              Dim [to] As String = Split([to_all], ";")(i)
              Dim [to_Address] As String = vbNullString, [to_DisplayName] As String = vbNullString
              If InStr([to], "<") > 0 Then
                [to_DisplayName] = Strings.Left([to], InStr([to], "<") - 1)
                [to_Address] = Strings.Right([to], Strings.Len([to]) - InStr([to], "<"))
                If InStr([to_Address], ">") > 0 Then [to_Address] = Strings.Left([to_Address], InStr([to_Address], ">") - 1)
              Else
                [to_Address] = [to]
              End If
              If (Strings.Len([to_Address]) > 0) AndAlso (Strings.Len([to_DisplayName]) > 0) Then
                If m_msg_UseUTF8 Then
                  .To.Add(New MailAddress([to_Address], [to_DisplayName], System.Text.Encoding.UTF8))
                Else
                  .To.Add(New MailAddress([to_Address], [to_DisplayName]))
                End If
              ElseIf Strings.Len([to_Address]) > 0 Then
                .To.Add(New MailAddress([to_Address]))
              End If
            Next
          End If
          If Strings.Len(m_msg_Cc) > 0 Then
            AddLogCDO(Chr(9) & Chr(9) & "CC:" & m_msg_Cc)
            Dim [cc_all] As String = m_msg_Cc
            For i As Integer = 0 To ChNum([cc_all], ";")
              Dim [cc] As String = Split([cc_all], ";")(i)
              Dim [cc_Address] As String = vbNullString, [cc_DisplayName] As String = vbNullString
              If InStr([cc], "<") > 0 Then
                [cc_DisplayName] = Strings.Left([cc], InStr([cc], "<") - 1)
                [cc_Address] = Strings.Right([cc], Strings.Len([cc]) - InStr([cc], "<"))
                If InStr([cc_Address], ">") > 0 Then [cc_Address] = Strings.Left([cc_Address], InStr([cc_Address], ">") - 1)
              Else
                [cc_Address] = [cc]
              End If
              If (Strings.Len([cc_Address]) > 0) AndAlso (Strings.Len([cc_DisplayName]) > 0) Then
                If m_msg_UseUTF8 Then
                  .CC.Add(New MailAddress([cc_Address], [cc_DisplayName], System.Text.Encoding.UTF8))
                Else
                  .CC.Add(New MailAddress([cc_Address], [cc_DisplayName]))
                End If
              ElseIf Strings.Len([cc_Address]) > 0 Then
                .CC.Add(New MailAddress([cc_Address]))
              End If
            Next
          End If
          If Strings.Len(m_msg_Bcc) > 0 Then
            AddLogCDO(Chr(9) & Chr(9) & "BCC:" & m_msg_Bcc)
            Dim [bcc_all] As String = m_msg_Bcc
            For i As Integer = 0 To ChNum([bcc_all], ";")
              Dim [bcc] As String = Split([bcc_all], ";")(i)
              Dim [bcc_Address] As String = vbNullString, [bcc_DisplayName] As String = vbNullString
              If InStr([bcc], "<") > 0 Then
                [bcc_DisplayName] = Strings.Left([bcc], InStr([bcc], "<") - 1)
                [bcc_Address] = Strings.Right([bcc], Strings.Len([bcc]) - InStr([bcc], "<"))
                If InStr([bcc_Address], ">") > 0 Then [bcc_Address] = Strings.Left([bcc_Address], InStr([bcc_Address], ">") - 1)
              Else
                [bcc_Address] = [bcc]
              End If
              If (Strings.Len([bcc_Address]) > 0) AndAlso (Strings.Len([bcc_DisplayName]) > 0) Then
                If m_msg_UseUTF8 Then
                  .Bcc.Add(New MailAddress([bcc_Address], [bcc_DisplayName], System.Text.Encoding.UTF8))
                Else
                  .Bcc.Add(New MailAddress([bcc_Address], [bcc_DisplayName]))
                End If
              ElseIf Strings.Len([bcc_Address]) > 0 Then
                .Bcc.Add(New MailAddress([bcc_Address]))
              End If
            Next
          End If
          If Strings.Len(m_msg_Subject) > 0 Then .Subject = m_msg_Subject
          If m_msg_UseUTF8 Then .SubjectEncoding = System.Text.Encoding.UTF8
          AddLogCDO(Chr(9) & Chr(9) & "Subject:" & .Subject.ToString)
          If Strings.Len(m_msg_TextBody) > 0 Then .Body = m_msg_TextBody
          If m_msg_UseUTF8 Then
            .BodyEncoding = System.Text.Encoding.UTF8
            AddLogCDO(Chr(9) & Chr(9) & "Encoding:" & .BodyEncoding.ToString)
          End If
          If Strings.Len(m_msg_Attachments) > 0 Then
            For i As Integer = 0 To ChNum(m_msg_Attachments, ";")
              Dim attach As String = Split(m_msg_Attachments, ";")(i)
              .Attachments.Add(New Attachment(attach))
              AddLogCDO(Chr(9) & Chr(9) & "Attachment:" & attach)
            Next
          End If
        End With
        AddLogCDO(Now.ToString & Chr(9) & "Configuring SMTP")
        Dim client As New SmtpClient()
        With client
          AddLogCDO(Chr(9) & Chr(9) & "Host=" & m_smtp_Host)
          If Strings.Len(m_smtp_Host) > 0 Then .Host = m_smtp_Host
          AddLogCDO(Chr(9) & Chr(9) & "Port=" & m_smtp_Port.ToString)
          .Port = m_smtp_Port
          If m_smtp_UseAuth And (Strings.Len(m_smtp_UserName) > 0) And (Strings.Len(m_smtp_Password) > 0) Then
            AddLogCDO(Chr(9) & Chr(9) & "useCredentials=1;userName=" & m_smtp_UserName & _
             ";password=" & StrDup(Strings.Len(m_smtp_Password), "*"))
            .Credentials = New System.Net.NetworkCredential(m_smtp_UserName, m_smtp_Password)
          Else
            AddLogCDO(Chr(9) & Chr(9) & "useCredentials=0")
          End If
          If m_smtp_UseSSL Then
            AddLogCDO(Chr(9) & Chr(9) & "EnableSsl=True")
            .EnableSsl = True 'использовать SSL
          Else
            AddLogCDO(Chr(9) & Chr(9) & "EnableSsl=False")
            .EnableSsl = False
          End If
          AddLogCDO(Chr(9) & Chr(9) & "Timeout=60sec")
          .Timeout = 60000
          AddLogCDO(Now.ToString & Chr(9) & "Configuring SMTP...Done")
          AddLogCDO(Now.ToString & Chr(9) & "Sending mail")
          .Send(message)
        End With
        AddLogCDO(Now.ToString & Chr(9) & "Sending mail...Done")
        AddLogCDO("-------------------------")
        Return True
      Catch
        str_error = "Error code: " & Err.Number & " (" & Err.Description & ")"
        AddLogCDO(Now.ToString & Chr(9) & "Sending mail...Failed. " & str_error)
        AddLogCDO("-------------------------")
      End Try
    End If
  End Function
End Module

'-----
  Public Sub AddLogCDO(ByVal str As String)
    Using file As System.IO.StreamWriter = _
       New System.IO.StreamWriter(IO.Path.Combine(Application.StartupPath, "maillog.txt"), True, System.Text.Encoding.UTF8)
      file.WriteLine(str)
      Debug.Print(str)
    End Using
  End Sub

  Public Function ChNum(ByVal the_str As String, ByVal ch As String) As Integer
    Dim count As Integer = 0
    For i As Integer = 0 To the_str.Length - 1
      If the_str(i) = ch Then count += 1
    Next
    Return count
  End Function
'