backscatter?

[testnburn]

hi everyone
weve recently deployed zimbra to replace our old mail system, all went well
though this past week, weve noticed an incredibly large number of mails getting deffered, although 90% is invalid mail.. it somehow affects incoming mail as weve received reports that it took hours to receive certain important mails..

here's part of the zimbra.log :
Apr 23 10:47:02 mailer postfix/smtp[26830]: D77482B7000B: to=<info@radio-info.ru>, relay=mail.radioinfo.ru[87.224.128.72]:25, delay=478, delays=0.12/348/51/78, dsn=4.0.0, status=deferred (host mail.radioinfo.ru[87.224.128.72] said: 478 severstroy2004@dinastia.ru no relay available (in reply to MAIL FROM command))
Apr 23 10:47:02 mailer postfix/smtp[20505]: 8421E2B7001F: to=<info@remodel-info.ru>, relay=mx1.leaderhost.ru[194.176.118.10]:25, delay=464, delays=0.25/434/30/0.42, dsn=5.0.0, status=bounced (host mx1.leaderhost.ru[194.176.118.10] said: 550 sorry, no mailbox here by that name (#5.1.1) (in reply to RCPT TO command))
Apr 23 10:47:03 mailer postfix/smtp[14179]: connect to remodomo.ru[217.16.28.65]:25: Connection refused
Apr 23 10:47:03 mailer postfix/smtp[14179]: 8421E2B7001F: to=<info@remodomo.ru>, relay=none, delay=465, delays=0.25/437/28/0, dsn=4.4.1, status=deferred (connect to remodomo.ru[217.16.28.65]:25: Connection refused)
Apr 23 10:47:03 mailer postfix/smtp[12390]: connect to mx1.masterhost.ru[217.16.16.81]:25: Connection timed out
Apr 23 10:47:03 mailer postfix/smtp[12390]: 855992B70020: to=<info@remnev.ru>, relay=none, delay=465, delays=0.14/408/57/0, dsn=4.4.1, status=deferred (connect to mx1.masterhost.ru[217.16.16.81]:25: Connection timed out)

searched the forum, found hits re: backscatter, but still having the same problem.
any help is greatly appreciated!

[testnburn]

additional logs from zimbra.log

Apr 23 12:01:12 mailer postfix/smtp[28693]: C91852B7009D: to=<info@ruletkaru.ru>, relay=none, delay=3997, delays=3370/534/93/0, dsn=4.4.1, status=deferred (connect to ruletkaru.ru[194.85.61.78]:25: Connection timed out)
Apr 23 12:01:12 mailer postfix/smtp[28714]: 06FF02B70039: to=<info@novyeoboi.ru>, relay=mx.yandex.ru[213.180.204.89]:25, delay=1599, delays=972/596/28/2.4, dsn=5.7.1, status=bounced (host mx.yandex.ru[213.180.204.89] said: 554 5.7.1 Message rejected under suspicion of SPAM (in reply to end of DATA command))
Apr 23 12:01:12 mailer postfix/smtp[28717]: C05F42B70115: to=<info@olimpokna.ru>, relay=static-240-164.domolink.elcom.ru[84.53.240.164]:25, delay=1060, delays=433/546/73/7.1, dsn=5.0.0, status=bounced (host static-240-164.domolink.elcom.ru[84.53.240.164] said: 554 Sorry, message looks like SPAM to me (in reply to end of DATA command))
Apr 23 12:01:12 mailer postfix/smtp[28456]: C05F42B70115: to=<info@olimpstar.ru>, relay=none, delay=1061, delays=433/567/60/0, dsn=4.4.1, status=deferred (connect to nmx11.masterhost.ru[90.156.155.115]:25: Connection timed out)
Apr 23 12:01:12 mailer postfix/smtp[28526]: 06FF02B70039: to=<info@novyi-urengoy.ru>, relay=none, delay=1600, delays=972/606/22/0, dsn=5.4.4, status=bounced (Host or domain name not found. Name service error for name=novyi-urengoy.ru type=A: Host not found)
Apr 23 12:01:12 mailer postfix/smtpd[5711]: connect from unknown[128.1.15.2]
Apr 23 12:01:12 mailer postfix/smtp[28370]: D5A342B70056: to=<info@startele.ru>, relay=none, delay=1663, delays=1036/584/42/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=startele.ru type=MX: Host not found, try again)
Apr 23 12:01:12 mailer postfix/smtp[28515]: D5A342B70056: to=<info@startender.ru>, relay=mail.startender.ru[82.146.59.142]:25, delay=1664, delays=1036/585/42/0.42, dsn=5.7.1, status=bounced (host mail.startender.ru[82.146.59.142] said: 550 5.7.1 <info@startender.ru>... Relaying denied. IP name lookup failed [121.58.195.147] (in reply to RCPT TO command))

[uxbod]

Have a read through Postfix Backscatter Howto for some ways of blocking.