How to set envelope sender (MAIL FROM) using exim

[Longman]

* Thomas Pircher wrote:
> Longman wrote:
>> For some reason a system I mail ignores the From address
>> and wants to reply to the return-path address despite there being no
>> Sender header present and the From being valid and deliverable.
> 
> This is IMHO the correct behaviour. You can write whatever you like in the
> From: field, but it is harder to lie in the envelope-from, if you are not
> the postmaster.

Is it correct behaviour for a system to say it was received from the
address cited in the return-path as opposed to the one in the From?

>> What solutions are there?
> 
> You can override the address on a per-user basis in /etc/email-addresses.
> At the moment I don't have access to an exim installation, but I think the
> syntax is the same as in /etc/aliases:
> user: email at example.com

I shall look into this email-addresses thingamajig. Thanks :)