I got remote mail server that for some reason don't accept connections
from my IP this way:
# nc mx.poczta.onet.pl 25
220-mx.poczta.onet.pl ESMTP
521 5.7.1 Service unavailable; client [5.9.116.9] blocked using
postscreenbl.opbl.onet.pl.
Which is fine but my exim drops email from queue silently, no delivery
attempt is logged and bounce is not generated which obviously is
terrible.