[Exim] Exim 3 - unroutable mail domain

Hello

Somebody can suppose why exim may not route sometimes to any domains,
and ever local?

Usually it does, but sometimes don't (i noticed, this happens when queue
runs):

2003-06-03 11:25:25 Start queue run: pid=13620
2003-06-03 11:25:25 19N5sQ-0003HJ-02 ** gladkih@???:
unrouteable mail domain "rfntr.neva.ru"
2003-06-03 11:25:25 19N6Af-0003Xj-00 <= <> R=19N5sQ-0003HJ-02 U=mail
P=local S=2782
2003-06-03 11:25:25 19N5sQ-0003HJ-02 Error message sent to sem@???
2003-06-03 11:25:25 19N5sQ-0003HJ-02 Completed
2003-06-03 11:25:25 19N6Af-0003Xj-00 ** sem@???: unrouteable mail
domain "iac.spb.ru"
2003-06-03 11:25:25 19N6Af-0003Xj-00 Frozen (delivery error message)
2003-06-03 11:25:25 19N5sP-0003HJ-01 ** geraskyn@???:
unrouteable mail domain "sigma-soft.spb.ru"
2003-06-03 11:25:25 19N6Af-0003Xm-00 <= <> R=19N5sP-0003HJ-01 U=mail
P=local S=2806
2003-06-03 11:25:25 19N5sP-0003HJ-01 Error message sent to sem@???
2003-06-03 11:25:25 19N5sP-0003HJ-01 Completed
2003-06-03 11:25:25 19N6Af-0003Xm-00 ** sem@???: unrouteable mail
domain "iac.spb.ru"
2003-06-03 11:25:25 19N6Af-0003Xm-00 Frozen (delivery error message)
2003-06-03 11:25:25 19N5s9-0003Fq-01 ** frost@???:
unrouteable mail domain "spb.cityline.ru"

All those domains are absolutely valid. The domain iac.spb.ru is local!

May be, MX-lookups fail? But resolv.conf contains 2 nameservers in the
same network, and they work. And how to trace those lookups on exim?

--
Regards,

Al Nikolov
Informational and Analytics Centre of Saint-Petersburg