Problem with exim rewriting rule

[Klaus Drews <klaus_drews@ngi.de>]

Hi there,

exim works fine with me, but produced one silly "bug" because of low -level
configuration. I wanted to replace my loginname with my original email-adress,
so that my ISP will accept the sender adress as correct. Therefore I created a
mail-address file and put the following into the rewriting rules section:
*@coma.coma.net    ${lookup{$1}lsearch{/etc/email-addresses}\
                                                {$value}fail} bcfrF
This part works fine.
The bug occurs, when I get mail from for example lpd for my local account. Then
the To-header will be changed and the mail will be delivered over my ISP instead
of directly to my local account.
But all I wanted was to change the From-header part.
Now I know, that I can do it with exim this way, but I do not know how. I tried a lot
and got lots of error messages.
Can someone fill me an example to do this and a short explanation ? I don't want it
to work without knowing why ... . (And please do not only refer to the docs. I read
them all - it helped little).

Thanks in advance,
Klaus.