This Outlook macro creates subfolders under the currently selected folder.

Use PowerShell to add or delete folders, using a list of folders in a text file: Create new Outlook folders using PowerShell

To use, create an Excel file with the desired folder names in one column with a header row. The folder names will begin with row 2 (cell A2). You can create the file in Notepad and save it with the CSV extension.

Use Set objParentFolder = objNewFolder to create nested folders.

Option Explicit

Public Sub MoveSelectedMessages()
    Dim objParentFolder As Outlook.Folder ' parent
    Dim newFolderName 'As String
    Dim strFilepath
    
    Dim xlApp As Object 'Excel.Application
    Dim xlWkb As Object ' As Workbook
    Dim xlSht As Object ' As Worksheet
    Dim rng As Object 'Range

    Set xlApp = CreateObject("Excel.Application")
    
    strFilepath = xlApp.GetOpenFilename
    If strFilepath = False Then
        xlApp.Quit
        Set xlApp = Nothing
        Exit Sub
    End If
      
    Set xlWkb = xlApp.Workbooks.Open(strFilepath)
    Set xlSht = xlWkb.Worksheets(1)
    Dim iRow As Integer
     
    iRow = 2
    
Set objParentFolder = Application.ActiveExplorer.CurrentFolder

While xlSht.Cells(iRow, 1) <> ""
newFolderName = xlSht.Cells(iRow, 1)
             
On Error Resume Next

Dim objNewFolder As Outlook.Folder
Set objNewFolder = objParentFolder.Folders(newFolderName)
 
If objNewFolder Is Nothing Then
    Set objNewFolder = objParentFolder.Folders.Add(newFolderName)
End If
    
    iRow = iRow + 1

 ' make new folder the parent
 ' Set objParentFolder = objNewFolder
    
  Set objNewFolder = Nothing
Wend
     
    xlWkb.Close
    xlApp.Quit
    Set xlWkb = Nothing
    Set xlApp = Nothing
    Set objParentFolder = Nothing
End Sub

Create subfolders at multiple levels

This code snippet uses the folder name in Column 1 to set the parent folder, with the new folder name in Column 2. Note that the parent folder needs to be the last one created (or the Inbox).

However, because the macro checks for the existence of the folder and creates it only if it doesn't exist, you can walk the folders to create deep subfolders. (Note: I never recommend deeply nested subfolders, it's too easy to forget where they are.)

A complete copy of this macro is here

'select starting parent
Set objParentFolder = Application.ActiveExplorer.CurrentFolder
 
Dim parentname

While xlSht.Cells(iRow, 1) <> ""
parentName = xlSht.Cells(iRow, 1)
newFolderName = xlSht.Cells(iRow, 2)
            
            
 If parentName = "Inbox" Then
 Set objParentFolder = Session.GetDefaultFolder(olFolderInbox)
    Else
 Set objParentFolder = objParentFolder.Folders(parentName)
 End If
On Error Resume Next

Dim objNewFolder As Outlook.Folder
Set objNewFolder = objParentFolder.Folders(newFolderName)

How to use macros

First: You will need macro security set to low during testing.

To check your macro security in Outlook 2010 or 2013, go to File, Options, Trust Center and open Trust Center Settings, and change the Macro Settings. In Outlook 2007 and older, it’s at Tools, Macro Security.

After you test the macro and see that it works, you can either leave macro security set to low or sign the macro.

Open the VBA Editor by pressing Alt+F11 on your keyboard.

To put the code in a module:

1. Right click on Project1 and choose Insert > Module
2. Copy and paste the macro into the new module.

More information as well as screenshots are at How to use the VBA Editor