MTAs and dialup connected machines

[Oskar Liljeblad <osk@hem.passagen.se>]

Hello

I have a little bit of a problem getting EXIM to work on
a dialup-connected computer.

The problem is that the local login name doesn't match
the login name on my email service provider (SMTP/POP3).
This causes problems when error mails are sent back
from remote MTAs. (Error-mails saying "user xxx doesn't
exist", "server is temporarily unavailable", etc.)

When I send email through the local MTA, Exim 3.03,
a Return-path: <usel@hem.passagen.se> is added.
This should really be <osk@hem.passagen.se> (that's
my public email address), but it's "usel" because that's
my local username.

So how do I solve it?

 1) Putting a "Reply-to: osk@hem.passagen.se" using the MUA
    does not help because MTAs send error mails to some other
    header (I assume Return-path).

 2) I could make my MTA rewrite the Return-path as 
    "osk@hem.passagen.se" instead of "usel@hem.passagen.se",
    but I don't know how/if it's even possible.

Please advise

Oskar Liljeblad (osk@hem.passagen.se)