After a lightning damage, I had to buy a new computer and therefor
install a new Linux. (PCI ISDN cards aren't supported by 2.0.35.)
It is now mostly working, but the most important thing still not
working, is that exim does not generate for each receipient a
file in the uucp spool. For the smaller mailing list, mailman pipes
in 3 mails and out come 40 mails, which are stored in the uucp spool.
(For the other mailing list this would be 300 mails.)
The only relevant options I found are batch, bsmtp and batch_max.
I tried different combinations of these with uucp_rsmtp_* and
uucp_rmail_*, but this did not change anything.