Possible bug in mailutils

Hi, I'd like to report what I believe is bug in mailutils.

For some time I've had a camera system that emails me an image file. The 
basic setup is a script that calls something like:

echo Motion detected - see http://cam1.example.com/camera | mail -s Test 
-A image.jpg -r "[email protected]" [email protected]

This sends an image from the camera along with a brief message which 
includes a link to the camera. This used to work fine; recently, 
however, after upgrading Linux versions the text of the message doesn't 
show up in the email.

**What used to happen*:* when I view the raw text of an old message from 
back when it used to work correctly, the message looks something like this:

---------------------------------------------------------------------------------------------------------------

--2006454085-1551307724=:11737 Content-ID: <20190227164844.11737@cam1> 
Content-Type: text/plain Motion detected - see 
http://cam1.example.com/camera --2006454085-1551307724=:11737 
Content-ID: <20190227164844.11737.1@cam1> Content-Type: 
application/octet-stream; name=image.jpg Content-Transfer-Encoding: 
base64 Content-Disposition: attachment; filename=image.jpg 
/9j/4QDeRXhpZgAATU0AKgAAAAgACAEAAAQAAAABAAAEAAEBAAQAAAABAAACQAEQAAIAAAAJAAAA 
bgEaAAUAAAABAAAAeAEbAAUAAAABAAAAgAEoAAMAAAABAAIAAAITAAMAAAABAAEAAIdpAAQAAAAB 
AAAAiAAAAABCcm9hZGNvbQAA ...

---------------------------------------------------------------------------------------------------------------

**What happens now*: *when I view the raw text of the message, I see 
something like this:

---------------------------------------------------------------------------------------------------------------

--2027169656-1581016592=:11969 Content-Type: text/plain; charset=UTF-8
Content-Disposition: attachment
Content-Transfer-Encoding: 8bit Content-ID: 
<20200206131632.11969.1@cam1> Motion detected - see 
http://cam1.example.com/camera --2027169656-1581016592=:11969 
Content-Type: application/octet-stream; name="image.jpg" 
Content-Disposition: attachment; filename="/var/www/html/image.jpg" 
Content-Transfer-Encoding: base64 Content-ID: 
<20200206131632.11969.1@cam1> 
/9j/4QDeRXhpZgAATU0AKgAAAAgACAEAAAQAAAABAAAEAAEBAAQAAAABAAADAAEQAAIAAAAJAAAA 
bgEaAAUAAAABAAAAeAEbAAUAAAABAAAAgAEoAAMAAAABAAIAAAITAAMAAAABAAEAAIdpAAQAAAAB 
AAAAiAAAAABCcm9hZGNvbQA ...

---------------------------------------------------------------------------------------------------------------

I think the line that I've highlighted in red above (3rd line - 
"Content-Disposition: attachment") is the problem. when I manually 
remove that line from the stored email on my server, everything appears 
correctly.

*When this started:* I think this may have changed in MailUtils 3.3. It 
was definitely working in Mailutils 3.1.1, but it does not work in the 
version that's in the current Raspbian Buster repository (which is 
Mailutils 3.5). I downloaded and compiled Mailutils 3.8, and it doesn't 
work right there either. I also tried 3.4 and 3.3 (didn't work) as well 
as 3.2 (did work).

I'm using Thunderbird as my mail reader. Other readers may handle this 
differently (in particular, Gmail seems to work around the problem).

Thanks - let me know if I'm doing something wrong or if I can provide 
more information.

ras