Change the value for email and ws. You might also want to change .Send to .Display to test. 

Option Explicit

Dim oOFs() As outlook.Folder


Sub SendReminder()
  Dim email$, v, item, i, ws As Worksheet, r As Range, c As Range, cc As Range
  'Tools > References > Microsoft Outlook xx.0 Object Library > OK
  Dim OL As outlook.Application, oMI As outlook.MailItem
  
  email = "ken@gmail.com"
  Set ws = Worksheets("SendReminder")
  Set r = ws.Range("I2", ws.Cells(ws.Rows.Count, "I").End(xlUp))
  
  Set OL = CreateObject("Outlook.Application")
  Erase oOFs()
  RecurseOFolders GetFolderPath(email, OL)
  
  For Each c In r
    Set oMI = Nothing
    Set cc = ws.Cells(c.Row, "P")
    If cc > Date Or cc = "" Then GoTo NextC
    For Each v In oOFs
      If v.Items.Count = 0 Then GoTo NextV
      For Each item In v.Items
        If TypeName(item) <> "MailItem" Then GoTo NextItem
        If item.SenderEmailAddress = c Then
          If oMI Is Nothing Then Set oMI = item
          If item.ReceivedTime > oMI.ReceivedTime Then Set oMI = item
        End If
NextItem:
      Next item
NextV:
    Next v
NextC:
    If Not oMI Is Nothing Then
      With oMI.Reply
        .Subject = ws.Cells(c.Row, "Q")
        .Body = ws.Cells(c.Row, "S") & vbCrLf & vbCrLf & ws.Cells(c.Row, "T") & .Body
          If ws.Cells(c.Row, "U") <> "" Then .Attachments.Add ws.Cells(c.Row, "U")
        .Send
      End With
    End If
  Next c
End Sub


Sub RecurseOFolders(CurrentFolder As outlook.MAPIFolder, _
  Optional skipTrash As Boolean = True)
  'Tools > References > Microsoft Outlook xx.0 Object Library > OK
  Dim i As Long, oOSF As outlook.MAPIFolder, oOF As outlook.Folder
  Dim ii As Long
 
  For i = CurrentFolder.Folders.Count To 1 Step -1
    Set oOF = CurrentFolder.Folders(i)
    If IsArray(oOFs) Then
      ii = UBound(oOFs) + 1
      Else: ii = 0
    End If
    If skipTrash And oOF.Name = "Trash" Then
      ii = ii - 1
      Else
      ReDim Preserve oOFs(ii)
      Set oOFs(ii) = oOF
    End If
  Next i
 
  For Each oOSF In CurrentFolder.Folders
    If oOSF.Name <> "Deleted Items" Then RecurseOFolders oOSF
  Next oOSF
End Sub


'Similar to, http://www.slipstick.com/developer/working-vba-nondefault-outlook-folders/#GetFolderPath
''Early Binding: Tools > References > Microsoft Outlook xx.0 Object Library > OK
Function GetFolderPath(ByVal FolderPath As String, oApp As outlook.Application) As outlook.Folder
    Dim oFolder As outlook.Folder
    Dim FoldersArray As Variant
    Dim i As Integer
     
    On Error GoTo GetFolderPath_Error
    If Left(FolderPath, 2) = "\\" Then
        FolderPath = Right(FolderPath, Len(FolderPath) - 2)
    End If
    'Convert folderpath to array
   FoldersArray = Split(FolderPath, "\")
    'Set oFolder = Application.Session.Folders.Item(FoldersArray(0))
   Set oFolder = oApp.Session.Folders.item(FoldersArray(0))
    If Not oFolder Is Nothing Then
        For i = 1 To UBound(FoldersArray, 1)
            Dim SubFolders As outlook.Folders
            Set SubFolders = oFolder.Folders
            Set oFolder = SubFolders.item(FoldersArray(i))
            If oFolder Is Nothing Then
                Set GetFolderPath = Nothing
            End If
        Next
    End If
    'Return the oFolder
   Set GetFolderPath = oFolder
    Exit Function
     
GetFolderPath_Error:
    Set GetFolderPath = Nothing
    Exit Function
End Function