Sent messages contain 'From nobody' header

[Ben Hancock]

Hi fellow Emacs users,

I compose mail in message-mode, and I set a default value for the FCC
header (to "~/mail/sent.rmail") to keep a copy of my sent messages.

On inspecting my sent messages -- either using rmail, or just viewing
the file as plain text -- I notice that each is prepended with a header
that looks like the following:

  From nobody Thu Feb  8 08:23:10 2024

The "From:" header (with a colon) is formed correctly; I have set the
variables user-full-name and user-mail-address. I am using the smtp
library to send mail, and as far as I can tell, this "From nobody"
header is not transmitted to the recipient. At least, it is not present
on inspecting messages I have sent myself.

This puzzles me. I have tried setting the EMAIL environment variable,
and setting the Emacs variable smtp-mail-address as well, with no
effect; the "From nobody" header still appears in my sent mail file.

What could be causing this?

Regards,

Ben

-- 
"In nature, we find no deficiency in respect of time,
nor any limitation with regard to power."
    --- James Hutton, Theory of the Earth