Pubblic Postfix IP Address always in CBL blacklist

Hi all,
i've a box with postfix, sasl auth and Mysql user database, place in
Italy.
This server manage an .ru domain, used by people locate in russian.
Always this IP was listed in the CBL blacklist, that many russian
servers use for control e-mail, and many of the e-mail sended at .ru
domain had problem.
The question is: there is something, about time zone or something like
this, that i MUST considerate when i place one server in Italy that
manage .ru domain? I mean about the fact that maybe some mail that
have send time different from the russian server, are considerate SPAM
and in time make my pubblic IP considered bad.
Thanks,
Mauro.