Andrea Monaco <andrea.monaco@autistici.org> writes:

> When I use C-c C-a (mml-attach-file) in message mode, a placeholder gets
> added to the message, something like "< # part ... < # / part>" (minus
> the spaces).
>
> If I copy and paste that tag to another message in a different buffer,
> will that message also include the attachment when sent?

You could try by sending such a mail to yourself ;-) But I think that
yes it will do.  You could also copy that "