running out of resource after calling lotus notes api many times~~

I wrote a robot program to call lotus notes API to send emails by different email a/c
the program works very well for the first few hours
but after around 4 hours, it is unable to call lotus notes API to call email (error in the following open function)

I suspect that I need to close / dispose the lotus notes API object.
but I have no ideas what need to close / dispose.

Could anyone help me, please?
Thanks!

Public Sub sendEmail()
 
 
        Dim recep As String() = ssMailTo
        Dim ccRecipient As String() = New String() {}
        Dim subj As String = sSubjectSend
        Dim mailbody As String = "This is robot message." '"hi" + ControlChars.NewLine + "bye"
 
        Dim savemsg As Boolean
 
        open()
 
 
        Dim domNotesDocumentMemo As NotesDocument
        Dim DomNotesItem As NotesItem
        Dim sUser As String
        Dim objNotesRichTextItem As NotesRichTextItem
 
 
 
        ' Create a new memo document.
        domNotesDocumentMemo = domDB.CreateDocument
 
 
        Call domNotesDocumentMemo.ReplaceItemValue("Form", "Memo")
        Dim body As NotesMIMEEntity
        'body = domNotesDocumentMemo.CreateMIMEEntity
        'body.CreateHeader("Subject").SetHeaderVal(subj)
        'body.CreateHeader("To").SetHeaderVal(String.Join(";", recep))
        'body.SetContentFromText _
        ' (Nothing, "text/plain;charset=UTF-8", MIME_ENCODING.ENC_NONE)
        body = domNotesDocumentMemo.CreateMIMEEntity
        Dim header As Domino.NotesMIMEHeader
        header = body.CreateHeader("Subject")
        Call header.SetHeaderVal(subj)
        header = body.CreateHeader("To")
        Call header.SetHeaderVal(String.Join(";", recep))
        header = body.CreateHeader("From")
        Call header.SetHeaderVal(domS.UserName)
        header = body.CreateHeader("Replyto")
        Call header.SetHeaderVal(domS.UserName)
 
 
        Call domNotesDocumentMemo.ReplaceItemValue("$INETReplyTo", domS.UserName)
        Call domNotesDocumentMemo.ReplaceItemValue("ReplyTo", domS.UserName)
        Call domNotesDocumentMemo.ReplaceItemValue("Principal", domS.UserName)
        Call domNotesDocumentMemo.ReplaceItemValue("$InetPrinicipal", domS.UserName)
        Call domNotesDocumentMemo.ReplaceItemValue("$AssistMail", Nothing)
        Call domNotesDocumentMemo.RemoveItem("$AssistMail")
        Call domNotesDocumentMemo.ReplaceItemValue("$TITLE", Nothing)
        Call domNotesDocumentMemo.ReplaceItemValue("InetSendTo", recep)
        'Call domNotesDocumentMemo.ReplaceItemValue("Form", "Memo")
        Call domNotesDocumentMemo.ReplaceItemValue("useApplet", "True")
        Call domNotesDocumentMemo.ReplaceItemValue("DefaultMailSaveOptions", "1")
        Call domNotesDocumentMemo.ReplaceItemValue("$StorageTo", "1")
        Call domNotesDocumentMemo.ReplaceItemValue("$Mailer", "Lotus Notes Release 6.5.4 March 27, 2005")
 
        'Call domNotesDocumentMemo.AppendItemValue("SendTo", "")
        ''Now get a handle on the item
        'DomNotesItem = domNotesDocumentMemo.GetFirstItem("SendTo")
        ''Now pass your array
        'For Each r As String In recep
        '    If r <> "" Then
        '        Call DomNotesItem.AppendToTextList(r)
        '    End If
        'Next
 
        Call domNotesDocumentMemo.ReplaceItemValue("SendTo", recep)
        Call domNotesDocumentMemo.ReplaceItemValue("CopyTo", ccRecipient)
 
        Call domNotesDocumentMemo.AppendItemValue("Subject", subj)
        'objNotesRichTextItem = domNotesDocumentMemo.CreateRichTextItem("Body")
 
        'Dim body As NotesMIMEEntity
        ''body = domNotesDocumentMemo.CreateMIMEEntity
        ''body.CreateHeader("Subject").SetHeaderVal(subj)
        ''body.CreateHeader("To").SetHeaderVal(String.Join(";", recep))
        ''body.SetContentFromText _
        '' (Nothing, "text/plain;charset=UTF-8", MIME_ENCODING.ENC_NONE)
        'body = domNotesDocumentMemo.CreateMIMEEntity
        'Dim header As Domino.NotesMIMEHeader
        'header = body.CreateHeader("Subject")
        'Call header.SetHeaderVal("MIME message")
        'header = body.CreateHeader("To")
        'Call header.SetHeaderVal("Roberta Person")
        'Dim stream As Domino.NotesStream
        'Call stream.WriteText("Text of message.")
        'Call body.SetContentFromText _
        '(stream, "text/plain;charset=UTF-8", MIME_ENCODING.ENC_NONE)
 
 
        'Call objNotesRichTextItem.AppendText(mailbody)
 
        If Trim(LCase(savemsg)) = "yes" Then
            domNotesDocumentMemo.SaveMessageOnSend = True
        Else
            domNotesDocumentMemo.SaveMessageOnSend = False
        End If
        domNotesDocumentMemo.Send(False)
        domNotesDocumentMemo = Nothing
 
        close()
 
    End Sub
 
 
 
 
 
 
 
    Public Function open() As Boolean
 
        IO.File.Copy(IO.Path.Combine(IO.Directory.GetCurrentDirectory, sIDfilePath), IO.Path.Combine(notesDataPath, sIDfilePath), True)
        IO.File.Copy(IO.Path.Combine(IO.Directory.GetCurrentDirectory, "notes.ini"), IO.Path.Combine(notesPath, "notes.ini"), True)
        WritePrivateProfileString("Notes", "KeyFilename", IO.Path.Combine(notesDataPath, sIDfilePath), IO.Path.Combine(notesPath, "notes.ini"))
        WritePrivateProfileString("Notes", "MailFile", sPfile, IO.Path.Combine(notesPath, "notes.ini"))
 
        domS = CreateObject("lotus.NotesSession")
 
 
        Call domS.Initialize(sPpassword)
        'System.Threading.Thread.Sleep(2000)
 
        'domDir = domS.GetDbDirectory(sPserver)
        'domDB = domDir.OpenMailDatabase()
        domDB = domS.GetDatabase(sPserver, sPfile)
        'domDir = domS.GetDbDirectory(sPserver).OpenMailDatabase
 
        'System.Threading.Thread.Sleep(2000)
 
 
        Return True
 
    End Function
 
    Public Sub close()
 
        domDB = Nothing
        domS = Nothing
 
        GC.Collect()
        GC.WaitForPendingFinalizers()
 
    End Sub

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