[exim] "Ghost" user running exim?

I have a problem with 4.63 (Debian exim4-daemon-heavy 4.63-3) that I am not
really sure how to describe, because it's too weird to me.

When _one_ specific user sends mail to my server, exim runs as a
non-existent user.

Oct 26 06:59:05 haven exim[28864]: 2006-10-26 06:59:05 H=mail.acc.umu.se
[130.239.18.156] U=postfix F=<dak@???> temporarily rejected RCPT
<bjorkriset-styrelse@???>: require_files: error for
/home/sympa/expl/listor.skyddsrummet.net/bjorkriset-styrelse/config:
Permission denied
haven:/etc/apache2/sites-available#

The problem is, I do not _have_ a "postfix" on my server.

haven:/home# grep -i postfix /etc/passwd
haven:/home#

When I try to send from another host, it works as expected (see log below)

Oct 25 23:36:35 haven exim[22132]: 2006-10-25 23:36:35 1GcqQN-0005ky-Hn <=
j2@mu
pp.net H=cookiemonster.mupp.net [10.4.3.2] P=esmtp S=2716
id=9CB5A76200029E439A4
4D2E52901D6A450EF@???
Oct 25 23:36:36 haven MailScanner[19103]: New Batch: Scanning 1 messages,
3139 b
ytes
Oct 25 23:36:36 haven MailScanner[19103]: Spam Checks: Starting
Oct 25 23:36:44 haven MailScanner[19103]: Message 1GcqQN-0005ky-Hn from
10.4.3.2
(j2@???) to listor.skyddsrummet.net is not spam, SpamAssassin (not
cached,
score=-0.74, required 6, autolearn=not spam, ALL_TRUSTED -1.44,
HTML_MESSAGE 0.
00, MIME_HTML_MOSTLY 0.70)
Oct 25 23:36:44 haven MailScanner[19103]: Spam Checks completed at 383 bytes
per
second
Oct 25 23:36:44 haven MailScanner[19103]: Virus and Content Scanning:
Starting
Oct 25 23:36:45 haven MailScanner[19103]: Virus Scanning completed at 2650
bytes
per second
Oct 25 23:36:45 haven MailScanner[19103]: Uninfected: Delivered 1 messages
Oct 25 23:36:45 haven MailScanner[19103]: Virus Processing completed at
95707 by
tes per second
Oct 25 23:36:45 haven MailScanner[19103]: Batch completed at 333 bytes per
secon
d (3139 / 9)
Oct 25 23:36:45 haven MailScanner[19103]: Batch (1 message) processed in
9.41 se
conds
Oct 25 23:36:46 haven exim[22143]: 2006-10-25 23:36:46 1GcqQN-0005ky-Hn =>
bjork
riset-styrelse <bjorkriset-styrelse@???> R=Sympa
a_Lists T=Sympa_Robots_Transport
Oct 25 23:36:46 haven exim[22143]: 2006-10-25 23:36:46 1GcqQN-0005ky-Hn
Complete
D

Here is the exim config for the transport/router

Sympa_Lists:
        driver = accept
        domains = +ListDomains
        require_files = /home/sympa/expl/$domain/$local_part/config
        transport = Sympa_Robots_Transport
        user = sympa
        group = sympa

Sympa_Robots_Transport:
        driver = pipe
        command = "/home/sympa/bin/queue $local_part@$domain"
        return_path_add
        delivery_date_add
        envelope_to_add
        user = sympa
        group = sympa
        current_directory = /home/sympa
        home_directory = /home/sympa

And the relevant part of the FS

haven:/home# ls -la
/home/sympa/expl/listor.skyddsrummet.net/bjorkriset-styrelse/
totalt 44
drwxr-x--- 4 sympa sympa 4096 2006-10-25 23:42 .
drwxr-x--- 6 sympa sympa 4096 2006-10-25 22:32 ..
drwxrwxr-- 2 sympa sympa 4096 2006-10-25 23:42 archives
-rw-r----- 1 sympa sympa  659 2006-10-25 22:38 config
-rw-r----- 1 sympa sympa  561 2006-10-25 22:32 config.0
-rw-r----- 1 sympa sympa  624 2006-10-25 22:33 config.1
-rw-r----- 1 sympa sympa   84 2006-10-25 23:47 include_admin_user.lock
-rw-r----- 1 sympa sympa    0 2006-10-25 22:35 include.lock
-rw-r----- 1 sympa sympa   34 2006-10-25 22:32 info
-rw-r----- 1 sympa sympa    8 2006-10-25 23:42 msg_count
drwxr-x--- 2 sympa sympa 4096 2006-10-25 22:32 shared
-rw-r----- 1 sympa sympa   30 2006-10-25 23:47 stats
haven:/home#