Run macro after new email

Try below

Private WithEvents Items As Outlook.Items

Private Sub Application_Startup()
    Dim Ns As Outlook.NameSpace
    Set Ns = Application.GetNamespace("MAPI")
    Set Items = Ns.GetDefaultFolder(olFolderInbox).Items
End Sub

Private Sub Items_ItemAdd(ByVal Item As Object)
    If TypeOf Item Is Outlook.MailItem Then
        Call RunExcelMacro
    End If
End Sub

Private Sub RunExcelMacro()
    Dim xlApp As Object
    Set xlApp = CreateObject("Excel.Application")
    xlApp.Workbooks.Open "C:\Workbook.xlsx"
    xlApp.Run "Import_Emails"
    xlApp.Quit
    Set xlApp = Nothing
End Sub