Often, you can find regular DNS requests from Windows machines. You can also use diald to control dialouts for DNS request. From time to time, the name server will query its forwarder, which will trigger a dialout. Since your ISP uses dynamic ip addresses, the request is sent out with the wrong ip address at startup of the dial-in connection. Therefore, no answer will be received.
Bind waits for one minute before resubmitting.
First you have to get sendmail to no long open any DNS connections. If you have a smarthost, you need to make sure that this name does not call the name server. The only catch is that when booting, mail that might still be in the queue will be sent by sendmail, even though the network is not yet up. Then when starting the samba daemon I gave it the internal IP address I use here at home. Since then a samba request is no longer sent to default, but stays here.