Re: rmail invalid mbox file

[Eli Zaretskii]

> From: Jim Erickson <jimerickso@gmail.com>
> Date: Wed, 05 May 2021 06:37:47 -0500
> 
> yes the first line of the mbox file reads as follows:
> 
> Return-Path: <jim@openbsd1.jimerickson.info>

That's the problem: the first line of each email message in an mbox
file should look something like this:

  From help-gnu-emacs-bounces+eliz=gnu.org@gnu.org Wed May 05 07:46:37 2021

That is, it must start with "From ", then a valid email address, then
date and time.  Return-Path: should be on the next line.

Do you have the "From " lines there, perhaps on lines after
Return-Path?  If so, maybe you could reorder the lines with Sed or
with Emacs, to get a usable mbox file.