You could use a TextBox in a UserForm and activate with something like:

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Target.Address = "$A$1" Then
UserForm1.Show
End If
End Sub



"Curious" wrote:

I am wondering if Excel allows a file (text file, or HTML file) to be
inserted to a cell. I know I can insert a comment. But I want to
attach a very long email chain to a cell, comment isn't quite
readable.

Thanks in advance.

H.Z.