When forwarding mails or replying, the Reply, Reply to All, Forward button expands a list of options e.g. “Forward with attachments” and “Forward”.
It is troublesome selecting the correct button when the mail to be forwarded is long and the user can not immediately see, if there is an attachment. The user can of course always select “Forward with attachments”, but this increases the mail server data volume or is a security problem because some attachments should not be forwarded to third parties.
Therefore I suggest to disable the option “Forward with attachments” (make it light grey), if there is no attachment available.