mail spam help

[gromsp]

Hy all,
i'm new to ispcp omega and ready to learn. Recently instaled ispcp omega 1.0.7 on debian server and everything works fine, but
Im my mail.log file i recently get a lot off log like this:

Aug 15 12:12:06 server postfix/qmgr[1135]: CCA58108B8BC: to=<prefeiturasfs@uol.com>, relay=none, delay=25640, delays=25618/21/0/0, dsn=4.4.1, status=deferred (delivery temporarily suspended: connect to uol.com[200.147.3.205]:25: Connection timed out)

I think someone is relaying spam mesages thru my mail server, but server is not an open relay. I'm realy confused and dont now what to check next and how to stop spam. I'm afraid that my mail server dont get to blacklist.

Thanks in advance

P.S. sory for my English