[exim] Waiting for Exim Banner

Hi,

I'm running exim4 for a while now, and it's really running fast. But
some customers complain, that sending a mail via our server takes
exactly 30 seconds before the connection has been established. I
tcpflow'ed the connection with the following result: Two pairs of
newlines will be sent during half a minute and after exactly 30 seconds
the SMTP-banner shows up. Then it's going on fast.

How can I find out, what's Exim doing during this pause? How can I stop
this?

Sincerly,
Christoph