[Exim] bogus bounces

It just started doing this. For a couple of days my list server
wasn't responding until I noticed that exim had crashed on it
and I restarted Exim.

When I sent emails to the list server, I get an _immediate_
bounce message saying "retry time not reached for any host
after a long failure period". There's something weird about a
"Long failure period" bounce coming back right away ...

I am able to send emails through the list server by using
telnet to port 25 on my list server box, but sending it via
my main email server, causes the bounce mentioned.

Any ideas?