Under SPAM hack attack

Hi to all, this is a very serious problem... in the few past days one of my servers is delivering A LOT of spam to different mailbox, I'm know for sure it was hack some how, I'm preparing a new install but... how can I stop that attack? were can I look? I'm short of knowledge right know.

Thanks to all!

 

PD: Here is a extract of the Mailq:

593D01FC274 2629 Mon Nov 17 10:55:52 [email protected]
(host mail-in.roc2.bluetie.com[208.89.132.202] said: 450 4.7.1 <[email protected]>: Recipient address rejected: Greylisting in action, please try again in 5 minutes. (in reply to RCPT TO command))
[email protected]
(host mx1.comcast.net[76.96.62.116] refused to talk to me: 554 IMTA09.westchester.pa.mail.comcast.net comcast 200.5.90.196 Comcast BL004 Blocked for spam. Please see http://help.comcast.net/content/faq/BL004)
[email protected]
[email protected]
(host mx2.optonline.net[167.206.4.79] refused to talk to me: 452 try later)
[email protected]
(host mailin-03.mx.aol.com[205.188.252.17] said: 421-: (DYN:T1) http://postmaster.info.aol.com/errors/421dynt1.html 421 SERVICE NOT AVAILABLE (in reply to end of DATA command))
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
(host b.mx.mail.yahoo.com[66.196.97.250] refused to talk to me: 421 4.7.0 [TS02] Messages from 200.5.90.196 temporarily deferred due to user complaints - 4.16.56.1; see http://postmaster.yahoo.com/421-ts02.html)
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
(connect to mail.wbia.net [65.14.23.101]: read timeout)
[email protected]

 

as i see you will need implement some spam defense, or your mailserver defense, try search fail2ban and set it to your distro. Will help