Hi
> Thank you so much for pointing this out!
> The original exim configuration/installation was done by a third party vendor > so again I made the mistake of assuming they knew what they were doing.
> For some reason they did set the return-path to <> but not the "From"
> address. I've changed this and hopefully the mail loop will not happen again.
This was probably meant and is fine.
The address given by RCPT TO is also known as "envelope-from", which needs
to be empty.
If some server replied to such a mail with anything, there is something
wrong on that side...