Sorry about that. It's not default on mine but it was an update install.

I confirm it should be unchecked by default, and the text should be "Add attachment info...".

I even doubt its usefulness at all. I don't know any mail client, local or online, which will not succeed displaying the attachment by itself.

Maybe it would be time to drop the text imposed with attachments. This an embarassment to me, I want my clients to read my messages and not software messages. And if there is an attachment they are warned by their own interface anyway.

Instead they have to see this, which has nothing whatsoever to do with our work conversations:

The following section of this message contains a file attachment
prepared for transmission using the Internet MIME message format.
If you are using Pegasus Mail, or any other MIME-compliant system,
you should be able to save it or view it from within your mailer.
If you cannot, please ask your system administrator for assistance.

Tools / Options / Sending mail - check the box 'Don't add attachment info sections...'

Isn't it a default setting now?