Tunneling smtp with exim4

[Jesper Holmberg <jesper.holmberg.5791@student.uu.se>]

I normally use exim4 with the "smarthost-configuration", i.e. I relay all
email to the mail server of my ISP. In the file
/etc/exim4/update-exim4.conf.conf i thus have a line saying:

dc_smarthost='mail.my.isp.se'

Now I would like to tunnel my outgoing email over ssh, and I have started
up an ssh tunnel with:

ssh -l jesper -L 1369:mail.my.isp.se:25 -N shell.my.isp.se

Then I changed the line in /etc/exim4/update-exim4.conf.conf to:

dc_smarthost='localhost:1369'

But this didn't work. I received the following email from my local exim4 server:

The following address(es) have yet to be delivered:
  jesper.holmberg.5791@student.uu.se: remote host address is the local host

Obviously exim4 doesn't want to send emails that it regards as remote to
local host. And how to make it consider a tunnel on the local host a
legitimate remote email server?

I have been looking through the config files of exim4, but nothing seems
like an obvious solution, does anyone here know how to solve this?

TIA,

Jesper