[exim] cannot get exim and cyrus to cooperarte

Hello,

I'm trying to set up an Exim MTA for use at our university and am
obviously running into some issues. We have attempted to set this up
before but given up after a while. No it becomes more urgent to
establish a new mail server at the institute. I'm starting from what I
suppose to be a more or less virgin exim/cyrus configuration since we
have overwritten previous attempts on a recent system update.

What I'm currently trying to achieve is receiving mails with Exim and
handing them over to cyrus to put them into the users inboxes. From the
standard configuration I followed the steps mentioned at
http://anfi.homeunix.org/exim/rtvcyrus.html to the best of my knowledge.
Here is my configuration:

/etc/cyrus.conf:
...
SERVICES {
         ...
         lmtp            cmd="lmtpd" listen="localhost:2003" prefork=0 
maxchild=20
         ...
}
...

/etc/exim4/conf.d/transport/55_cyrus_ltcp:
cyrus_ltcp:
         driver = smtp
         protocol = lmtp
         hosts = localhost
         port = 2003
         allow_localhost

/etc/exim4/conf.d/router/055_cyrus_vdom:
cyrus_vdom:
         driver = accept
         domains = +cyrus_domains
         transport = cyrus_ltcp
         no_more

I was not quite sure where, why and to what I had to set the
cyrus_domains list. So I added it where I found other domain lists and
set it to the domains that exim4 should be responsible for receiving
(krist-test.uni-erlangen.de currently). Hope this is correct?
/etc/exim4/conf.d/main/01_exim4-confi_listmacrosdefs:
# List of domains considered local for exim. Domains not listed here
# need to be deliverable remotely.
domainlist local_domains = MAIN_LOCAL_DOMAINS
# cyrus domains
domainlist cyrus_domains = krist-test.uni-erlangen.de :
krist.uni-erlangen.de

I also skipped step 4 of the howto as it does not appear to be necessary
for getting it working in the first place.

Then I rebuild the config, restart exim4 and cyrus and attempt to send
an e-mail to an (existing) inbox "user.klimczak" by writing to
klimczak@???.

This is what I see in /var/log/exim4/mainlog then (I just blacked out my
private sending addresse:
2010-10-26 14:01:10 1PAiDG-0004wb-TZ <= SENDERADDRESSE
H=mx-rz-smart.rrze.uni-erlangen.de (mx-rz-1.rrze.uni-erlangen.de)
[131.188.11.20] P=esmtp S=2349 id=4SENDERID
2010-10-26 14:01:10 1PAiDG-0004wb-TZ ==
klimczak@??? R=cyrus_vdom T=cyrus_ltcp defer
(-45): SMTP error from remote mail server after MAIL
FROM:<SENDERADDRESSE> SIZE=3414: host localhost.physik.uni-erlangen.de
[127.0.0.1]: 430 Authentication required

I do not quite understand -- judging from the howto -- where
authorization should be required and how to achieve it.

Any help would be appreciated. Maybe someone can tell me what I'm doing
wrong or how to get more detailed error information from the system.

Best regards,
micha