VBA macro to file sent mails

Hello. Indeed, your original macro doesn’t work with Gmail because Outlook respects the SaveSentMessageFolder property only for Exchange accounts. Since your Gmail account is likely set up as IMAP, Outlook ignores this setting and always saves sent emails in the default "Sent Mail" folder.

Try using this:

Option Explicit
' Module-level variable to hold the folder chosen before send
Private gTargetFolder As Outlook.MAPIFolder
Private Sub Application_ItemSend(ByVal Item As Object, Cancel As Boolean)
    If TypeOf Item Is Outlook.MailItem Then
        Dim acc As Outlook.Account
        Set acc = Item.SendUsingAccount
        
        If acc Is Nothing Then Exit Sub
        
        Set gTargetFolder = Application.Session.PickFolder
        If gTargetFolder Is Nothing Then Exit Sub ' User cancelled folder pick
        
        If acc.AccountType = olExchange Then
            ' Exchange accounts: set folder, Outlook handles saving
            Set Item.SaveSentMessageFolder = gTargetFolder
            Set gTargetFolder = Nothing ' Clear after use
        Else
            ' Non-Exchange accounts: cannot set SaveSentMessageFolder
            ' Sent mail will be saved in default Sent Items
            ' We'll move it later in ItemSendComplete
            Set Item.SaveSentMessageFolder = Nothing
            ' gTargetFolder remains set for use in ItemSendComplete
        End If
    End If
End Sub
Private Sub Application_ItemSendComplete(ByVal Item As Object)
    On Error Resume Next
    
    If gTargetFolder Is Nothing Then Exit Sub ' No folder selected or Exchange case
    
    If TypeOf Item Is Outlook.MailItem Then
        Dim acc As Outlook.Account
        Set acc = Item.SendUsingAccount
        
        If acc Is Nothing Then Exit Sub
        
        ' Only process non-Exchange accounts
        If acc.AccountType <> olExchange Then
            Dim sentFolder As Outlook.MAPIFolder
            Set sentFolder = Application.Session.GetDefaultFolder(olFolderSentMail)
            
            ' Confirm the sent mail is currently in Sent Items (default)
            If Item.Parent.EntryID = sentFolder.EntryID Then
                ' Move the sent mail to the user-chosen folder
                Item.Move gTargetFolder
            End If
        End If
    End If
    
    Set gTargetFolder = Nothing ' Clear for next send
End Sub

This macro works basically the same, the only difference is that for Exchange, Outlook saves sent mail directly to your chosen folder; for Gmail, the macro must move it afterward because Outlook always saves to the default Sent folder (that's how it handles IMAP configuration).

Let me know if this works for you or if you see any error.

Thank you very much! It works on the Exchange account and on the Gmail account the window with the folder pops up, but then I get a run-time error (I am pasting the screenshot below).
The error is on the code line Set Item.SaveSentMessageFolder = Nothing

Any idea how that can be fixed?

Thanks again!