[subfolders in outlook]

hello,

You can do that via VBA. I find a article online which may be just what you want. Below is the codes:

Sub ExpandAllMailFolders()
    Dim objCurrentFolder As Outlook.Folder
    Dim objPSTFolders As Outlook.Folders
    Dim objFolder As Outlook.Folder

    Set objCurrentFolder = Application.ActiveExplorer.CurrentFolder
    'Specify a specific pst file
    'Change "PSTName" to the name of your own Outlook PST file
    Set objPSTFolders = Application.Session.Folders("PSTName").Folders
 
    For Each objFolder In objPSTFolders
        Call ProcessFolder(objFolder)
    Next

    DoEvents
    Set Application.ActiveExplorer.CurrentFolder = objCurrentFolder
End Sub

Sub ProcessFolder(ByVal objCurFolder As Outlook.Folder)
    Dim objSubfolder As Outlook.Folder
 
    'Only expand the mail folders
    If objCurFolder.DefaultItemType = olMailItem Then
       Set Application.ActiveExplorer.CurrentFolder = objCurFolder
       DoEvents
 
       'Process all subfolders recursively
       If objCurFolder.Folders.Count > 0 Then
          For Each objSubfolder In objCurFolder.Folders
              Call ProcessFolder(objSubfolder)
          Next
       End If
    End If
End Sub

you can create a  button for this macro. so you can click the button to expand all subfolders. And here is the link of the article

 

https://www.datanumen.com/blogs/quickly-expand-collapse-mail-folders-outlook/

 

Hope it helps