[Exim] accept failures

Some of our customers had the following problem:

They came from a dial-up connection of some provider
and tried to deliver their mail to our mail server.
But they could not get a connection. I let them try
a telnet session on port 25 which also failed with
"no connection". Since other people had no problems
I guess they had a problem with their provider.

But...

1999-08-08 22:44:27 4 accept() failures: No route to host

...this was all there was in the mainlog.
I didn't realize this failure had something to do with
their try of delivering.

So what does that error message excactly meen?
I haven't found something about that in the FM ;-)
--
Torsten