re; stopping spam attacks

I would like to know how to prevent this sort of mail bombing from happening:
May 21 00:47:16 rhfs1 postfix/smtp[12132]: connect to mx3.compuserve.com[149.174.40.5]: Connection refused (port 25)
May 21 00:47:17 rhfs1 postfix/smtp[12132]: connect to mx3.compuserve.com[149.174.40.6]: Connection refused (port 25)
May 21 00:47:17 rhfs1 postfix/smtp[12151]: BF5DF14AB8E: to=<[email protected]>, relay=mailin-04.mx.aol.com[64.12.138.152], delay=5, status=sent (250 OK)
May 21 00:47:17 rhfs1 postfix/smtp[12132]: connect to mx1.compuserve.com[149.174.40.4]: Connection refused (port 25)
May 21 00:47:17 rhfs1 postfix/smtp[12110]: connect to mx1.mail.lycos.com[209.202.220.135]: Connection timed out (port 25)
May 21 00:47:17 rhfs1 postfix/smtp[12132]: connect to mx1.compuserve.com[149.174.40.134]: Connection refused (port 25)
May 21 00:47:18 rhfs1 postfix/smtpd[12244]: connect from rhfs1[192.168.1.10]
May 21 00:47:18 rhfs1 postfix/smtpd[12244]: 42D8E14AB8E: client=rhfs1[192.168.1.10]
May 21 00:47:18 rhfs1 postfix/cleanup[12245]: 42D8E14AB8E: message-id=<[email protected]>
May 21 00:47:18 rhfs1 postfix/nqmgr[11365]: 42D8E14AB8E: from=<[email protected]>, size=2422, nrcpt=1 (queue active)
May 21 00:49:42 rhfs1 postfix/nqmgr[11365]: F316E14ABE6: from=<>, size=4166, nrcpt=1 (queue active)
May 21 00:49:46 rhfs1 postfix/smtp[12110]: F316E14ABE6: to=<[email protected]>, relay=mx1.mail.yahoo.com[64.156.215.6], delay=5, status=bounced (host mx1.mail.yahoo.com[64.156.215.6] said: 553 VS10-RT Possible forgery or deactivated due to abuse (#5.1.1))
May 21 00:49:47 rhfs1 postfix/smtp[12153]: 0841D14ABE4: to=<[email protected]>, relay=pbimailc.prodigy.net[207.115.63.107], delay=10, status=bounced (host pbimailc.prodigy.net[207.115.63.107] said: 553 5.3.0 DNSBL:You are listed at relays.osirusoft.com)
May 21 00:49:47 rhfs1 postfix/cleanup[12245]: 71A9714ABE5: message-id=<[email protected]>
May 21 00:49:47 rhfs1 postfix/nqmgr[11365]: 71A9714ABE5: from=<>, size=4147, nrcpt=1 (queue active)
May 21 00:49:48 rhfs1 postfix/smtp[12132]: 71A9714ABE5: to=<[email protected]>, relay=mx2.mail.yahoo.com[64.157.4.78], delay=1, status=bounced (host mx2.mail.yahoo.com[64.157.4.78] said: 553 VS10-RT Possible forgery or deactivated due to abuse (#5.1.1))
May 21 00:49:49 rhfs1 postfix/smtp[12136]: DCA7C14ABDD: to=<[email protected]>, relay=mx1.compuserve.com[149.174.40.4], delay=88, status=sent (250 2.0.0 h4KGsvhV000740 Message accepted for delivery)

Currently using rhl7.3 with postfix-1.1.7-2.
This is a printout of the port scan I did on the server using nmap

(The 1534 ports scanned but not shown below are in state: closed)
Port       State       Service
22/tcp     open        ssh
25/tcp     open        smtp
53/tcp     open        domain
110/tcp    open        pop-3
6000/tcp   filtered    X11                <- would like to not see these ports below as "filtered ports".  Perfer not to see them at all.
12345/tcp  filtered    NetBus          <- Is this possible?
12346/tcp  filtered    NetBus
31337/tcp  filtered    Elite


/etc/postfix/master.cf (sniped)

# service type  private unpriv  chroot  wakeup  maxproc command + args
#               (yes)   (yes)   (yes)   (never) (50)
# ==========================================================================
#smtp   inet    n       -       y       -       -       smtpd
2500    inet    n       -       n       -       -       smtpd  <- used for Sophos MailMonitor


Thanks

Jon L. Miller, MCNE, CNS
Director/Sr Systems Consultant
MMT Networks Pty Ltd
http://www.mmtnetworks.com.au

"I don't know the key to success, but the key to failure
 is trying to please everybody." -Bill Cosby