[exim] Strange problem

Hello,

we've a strange problem with our central mail relay.

We allow unauthenticated relaying for all hosts in our network (130.149.0.0/16),
which works. But today the following problem came up for one user:

Exim log shows:

2012-07-10 14:08:42 H=pc-45-77.isr.tu-berlin.de [130.149.45.77] F=<source@???> rejected RCPT <destination@???>: relay not permitted, authentication required

Ups, this IP is from our network! Needs investigation.

[root@mailfrontend-4 /]# exim_checkaccess 130.149.45.77 destination@??? -f source@???
Accepted
[root@mailfrontend-4 /]#

Oha!

And furthermore "exim -d -bhc 130.149.45.77" ends with

..
processing "accept"
check hosts = +relay_hosts : !+smtpauth_hosts
cached yes match for +relay_hosts
cached lookup data = NULL
host in "+relay_hosts : !+smtpauth_hosts"? yes (matched "+relay_hosts" - cached)
accept: condition test succeeded
SMTP>> 250 Accepted


What's this?


Kind regards,
Frank Elsner