Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

Our firewall failed about 3 weeks ago and while it was being replaced we were placed on the “cbl.abuseat.org” spam blacklist. Once we got the new firewall in and configured we were able to get unlisted. Now about 2 weeks later we are listed again. Here is our config info and what we have tried.

Win2K3 - Exchange 2003 which goes through the firewall. The firewall was set to deny all out going SMTP traffic except for SMTP traffic (originally not restricted to port 25) from our exchange server. Our 110 client XP machines are running McAfee and set to not allow sending of smtp traffic (I have seen this work, so am fairly confident it is working). That was good enough until yesterday when we were blacklisted again.

Working with our firewall vendor we now only allow SMTP traffic on port 25 from the exchange server. All other SMTP traffic is blocked from leaving our network. It appears that mail was going out on strange ports such as .23111 from our exchange server, is that correct (see first set of log info)? But I am not sure from the latest logs if that has been fixed. Also, can spam bots send spam through an exchange server on port 25? If so can it be stopped without finding the spam bot? We are looking for the spam bot but not having any luck yet.

Thanks for any help.

I ran tcpdump and got the following info before we made the latest firewall changes:

16:54.8 IP  exchange-server.our-domain.com.23111 > s5a1.psmtp.com.25:   Flags   [.], ack 263, win 65273, length 0
16:55.7 IP  s5a1.psmtp.com.25 > exchange-server.our-domain.com.23111:   Flags   [P.], ack 4221, win 14600, length 12
16:55.7 IP  exchange-server.our-domain.com.23111 > s5a1.psmtp.com.25:   Flags   [P.], ack 275, win 65261, length 6
16:56.0 IP  s5a1.psmtp.com.25 > exchange-server.our-domain.com.23111:   Flags   [P.], ack 4221, win 14600, length 12
16:56.0 IP  exchange-server.our-domain.com.23111 > s5a1.psmtp.com.25:   Flags   [.], ack 275, win 65261, length 0
16:56.1 IP  s5a1.psmtp.com.25 > exchange-server.our-domain.com.23111:   Flags   [P.], ack 4227, win 14600, length 21
16:56.1 IP  s5a1.psmtp.com.25 > exchange-server.our-domain.com.23111:   Flags   [F.], seq 296, ack 4227, win 14600, length 0
16:56.1 IP  exchange-server.our-domain.com.23111 > s5a1.psmtp.com.25:   Flags   [.], ack 297, win 65240, length 0
16:56.1 IP  exchange-server.our-domain.com.23111 > s5a1.psmtp.com.25:   Flags   [F.], seq 4227, ack 297, win 65240, length 0
16:56.6 IP  s5a1.psmtp.com.25 > exchange-server.our-domain.com.23111:   Flags   [.], ack 4228, win 14600, length 0
16:57.7 IP  exchange-server.our-domain.com.23257 > pineapp.hcsmail.co   m.25:   Flags [S], seq 3560091943, win 65535, options [mss 1460,nop,nop,sackOK], length 0
16:58.0 IP  pineapp.hcsmail.com.25 > exchange-server.our-domain.com.2   3257:00:00  Flags [S.], seq 3962637029, ack 3560091944, win 5840, options [mss 1380,nop,nop,sackOK], length 0
16:58.0 IP  exchange-server.our-domain.com.23257 > pineapp.hcsmail.co   m.25:   Flags [.], ack 1, win 65535, length 0
16:58.1 IP  pineapp.hcsmail.com.25 > exchange-server.our-domain.com.2   3257:00:00  Flags [P.], ack 1, win 5840, length 20
16:58.1 IP  exchange-server.our-domain.com.23257 > pineapp.hcsmail.co   m.25:   Flags [P.], ack 21, win 65515, length 33
16:58.2 IP  pineapp.hcsmail.com.25 > exchange-server.our-domain.com.2   3257:00:00  Flags [.], ack 34, win 5840, length 0
16:58.2 IP  pineapp.hcsmail.com.25 > exchange-server.our-domain.com.2   3257:00:00  Flags [P.], ack 34, win 5840, length 20

This is what I got after the firewall changes:

01:52.6 IP  our-exchange.our-domain.com.17177 > our-domaincontroller.our-domain.com.53: 12044+ A? mail.painclinic-nw.com. (40)  
01:52.6 IP  our-exchange.our-domain.com.15727 > our-domaincontroller.our-domain.com.53: 12285+ A? mail.snyders-han.com. (38)    
01:52.7 IP  99-53-214-98.lightspeed.genvil.sbcglobal.net.1770 > our-exchange.our-domain.com.443: Flags [.], ack 570, win 16380, length 0
01:52.9 IP  204-0.202-68.tampabay.res.rr.com.58065 > our-exchange.our-domain.com.443: Flags [P.], ack 1, win 17477, length 49   
01:52.9 IP  204-0.202-68.tampabay.res.rr.com.58065 > our-exchange.our-domain.com.443: Flags [P.], ack 1, win 17477, length 197  
01:52.9 IP  our-exchange.our-domain.com.443 > 204-0.202-68.tampabay.res.rr.com.58065: Flags [.], ack 1503, win 64573, length 0  
01:52.9 IP  our-exchange.our-domain.com.443 > 204-0.202-68.tampabay.res.rr.com.58068: Flags [P.], ack 1, win 64649, length 149  
01:52.9 IP  ggadke.our-domain.com.1203 > our-exchange.our-domain.com.1025: Flags [.], ack 1, win 65016, length 1        
01:52.9 IP  our-exchange.our-domain.com.1025 > ggadke.our-domain.com.1203: Flags [.], ack 1, win 65269, length 0        
01:52.9 IP  dwhite.our-domain.com.1215 > our-exchange.our-domain.com.1025: Flags [.], ack 1631, win 65535, length 1     
01:52.9 IP  our-exchange.our-domain.com.1025 > dwhite.our-domain.com.1215: Flags [.], ack 2574, win 64590, length 0     
01:52.9 IP  vbejin.our-domain.com.1282 > our-exchange.our-domain.com.1025: Flags [.], ack 1, win 64548, length 1            
01:52.9 IP  our-exchange.our-domain.com.1025 > vbejin.our-domain.com.1282: Flags [.], ack 1, win 64769, length 0            
01:53.0 IP  204-0.202-68.tampabay.res.rr.com.58065 > our-exchange.our-domain.com.443: Flags [P.], ack 1, win 17477, length 49   
01:53.0 IP  our-storagedevice.our-domain.com.123 > our-exchange.our-domain.com.123: NTPv3, symmetric active, length 68      
01:53.0 IP  our-exchange.our-domain.com.21059 > our-domaincontroller.our-domain.com.53: 34757+ PTR? 9.1.168.192.in-addr.arpa. (42)
01:53.0 IP  our-domaincontroller.our-domain.com.53 > our-exchange.our-domain.com.21059: 34757* 1/0/0 PTR[|domain]       
01:53.0 AR  P, Request who-has our-storagedevice.our-domain.com tell our-exchange.our-domain.com, length 28         
01:53.0 IP  our-exchange.our-domain.com.123 > our-storagedevice.our-domain.com.123: NTPv3, Server, length 68            
01:53.1 AR  P, Reply our-storagedevice.our-domain.com is-at 00:15:17:22:b2:44 (oui Unknown), length 92              
01:53.1 IP  99-53-214-98.lightspeed.genvil.sbcglobal.net.1775 > our-exchange.our-domain.com.443: Flags [P.], ack 1, win 17477, length 41
01:53.1 IP  our-exchange.our-domain.com.443 > 204-0.202-68.tampabay.res.rr.com.58065: F                 

Here is part of a smtp log from the exchange server:

7/2/2010 17:36:15 64.18.6.14 OutboundConnectionResponse SMTPSVC1 our-exchange - 25 - - 220+Postini+ESMTP+225+y6_29_1c0+ready.++CA+Business+and+Professions+Code+Section+17538.45+forbids+use+of+this+system+for+unsolicited+electronic+mail+advertisements. 0 0 164 0 78 SMTP - - - -

7/2/2010 17:36:15 64.18.6.14 OutboundConnectionCommand SMTPSVC1 our-exchange - 25 EHLO - our-exchange.Northwoods.com 0 0 4 0 78 SMTP - - - -

7/2/2010 17:36:15 64.18.6.14 OutboundConnectionResponse SMTPSVC1 our-exchange - 25 - - 250-Postini+says+hello+back 0 0 27 0 172 SMTP - - - -

7/2/2010 17:36:15 64.18.6.14 OutboundConnectionCommand SMTPSVC1 our-exchange - 25 MAIL - FROM: 0 0 4 0 172 SMTP - - - -

7/2/2010 17:36:15 64.18.6.14 OutboundConnectionResponse SMTPSVC1 our-exchange - 25 - - 250+Ok 0 0 6 0 250 SMTP - - - -

7/2/2010 17:36:15 64.18.6.14 OutboundConnectionCommand SMTPSVC1 our-exchange - 25 RCPT - TO: 0 0 4 0 250 SMTP - - - -

7/2/2010 17:36:15 64.18.6.14 OutboundConnectionResponse SMTPSVC1 our-exchange - 25 - - 250+Ok 0 0 6 0 782 SMTP - - - -

7/2/2010 17:36:15 64.18.6.14 OutboundConnectionCommand SMTPSVC1 our-exchange - 25 DATA - - 0 0 4 0 782 SMTP - - - -

7/2/2010 17:36:15 64.18.6.14 OutboundConnectionResponse SMTPSVC1 our-exchange - 25 - - 354+Feed+me 0 0 11 0 860 SMTP - - - -

7/2/2010 17:36:17 64.18.6.14 OutboundConnectionResponse SMTPSVC1 our-exchange - 25 - - 250+Thanks 0 0 10 0 1657 SMTP - - - -

7/2/2010 17:36:17 64.18.6.14 OutboundConnectionCommand SMTPSVC1 our-exchange - 25 QUIT - - 0 0 4 0 1672 SMTP - - - -

7/2/2010 17:36:17 64.18.6.14 OutboundConnectionResponse SMTPSVC1 our-exchange - 25 - - 221+Catch+you+later 0 0 19 0 1735 SMTP - - - -

7/2/2010 17:37:09 208.65.144.247 p01c11m094.mxlogic.net SMTPSVC1 our-exchange gateway IP 0 EHLO - #NAME? 250 0 320 27 0 SMTP - - - -

7/2/2010 17:37:09 208.65.144.247 p01c11m094.mxlogic.net SMTPSVC1 our-exchange gateway IP 0 MAIL - +FROM: 250 0 108 95 0 SMTP - - - -

7/2/2010 17:37:09 208.65.144.247 p01c11m094.mxlogic.net SMTPSVC1 our-exchange gateway IP 0 RCPT - +TO: 250 0 41 38 0 SMTP - - - -

7/2/2010 17:37:09 208.65.144.247 p01c11m094.mxlogic.net SMTPSVC1 our-exchange gateway IP 0 DATA - +<5db32eec-3b06-4e97-8b34-6c147ac35b0a@xtinmta11.xt.local> 250 0 141 22978 281 SMTP - - - -

7/2/2010 17:37:09 208.65.144.247 p01c11m094.mxlogic.net SMTPSVC1 our-exchange gateway IP 0 QUIT - p01c11m094.mxlogic.net 240 515 75 4 0 SMTP - - - -

share|improve this question
add comment

3 Answers 3

Hmmm... where to start.

Your Exchange server doesn't make outbound SMTP connections to other email servers FROM port 25, it makes those outbound connections TO port 25. This is the way all TCP\IP hosts operate regardless of the service in question (for the most part, but for this argument consider this to be the case). Exchange uses a local port in the ephemeral port range as it's outgoing port and it connects to another email server on that servers' port 25. This works in reverse when other email servers connect to your Exchange server to send you email, the other server connects from one of it's ephemeral ports to port 25 on your Exchange server.

Why do you think the firewall is relevant to this problem? When the firewall failed did you not have a replacement firewall in place? What was protecting your network while you waited for the new firewall?

If any of your workstations are infected with malware then they're at risk for sending spam through the Exchange server via MAPI or SMTP (depending on how the workstations and the Exchange server are configured), or from themselves.

Merely having a firewall in front of your Exchange server doesn't have anything to do with whether or not your outbound mail will be flagged as Spam or whether or not your Exchange servers' outbound ip address will be blacklisted. External email servers have no way of detecting whether or not your Exchange server is behind a firewall. A firewall may reduce the likelihood of being blacklisted by restricting outbound SMTP traffic to just that from the Exchange server, which presumably is not being used as a relay.

Your first tcpdump shows the TCP session information for what is presumably an SMTP communication session but gives you no information regarding that SMTP session and is therefore almost worthless in troubleshooting your problem.

Your second tcpdump doesn't show any SMTP connection that I could find and is therefore worthless in troubleshooting your problem.

All that being said, here are a couple of pointers:

Make sure your Exchange servers outbound greeting matches the FQDN for your public MX record.

Make sure to set up a PTR record in your public DNS for the FQDN of the Exchange server.

Make sure to set up an SPF record in your public DNS.

Restrict all outbound communication TO port 25 for all internal hosts except your Exchange server.

None of these are guaranteed to keep you off of the blacklists, but they're helpful in that regard.

As a final note, enable SMTP logging on your Exchange server so that you'll have a log record of all inbound and outbound SMTP sessions. This is invaluable in troubleshooting SMTP problems.

share|improve this answer
    
Thanks for clarifying the port usage. I thought if we blocked all outgoing smtp traffic from our network out that would prevent spam from an infected pc. By only allowing smtp traffic on port 25 from just our exchange server I believed that would narrow down where the spam may be coming from. But if I understand correctly it could still come from an infected pc through the mapi or smtp via the exchange server. No we didn't have a spare FW so we were without for about 6 hours until we got a temp one from a local store while waiting for the overnight replacement. –  PBK Jul 2 '10 at 18:42
    
Because the clients send through Exchange, your Exchange server can become an unwitting spambot for an infected machine. I would advise running a full malware scan on all of your machines. –  joeqwerty Jul 2 '10 at 18:51
add comment

Not a lot to go on here, but CBL will only list you because you have infrastructure which has been used by spam senders. That might mean you are sending out spam, but it might also mean that you have an open proxy (HTTP, Socks or other) or you may have a vulnerable html form on a website you are hosting. CBL should give some idea as to why you were listed.

If your machines are sending out spam then you should probably have a default deny-all policy on your firewall, closely monitor both allowed and denied traffic and only open ports when you are sure nothing is attempting to send out on those machines. You should also take a look at what ports you have open externally to make sure nobody is using any form of proxies, and you should make sure any websites you are hosting are secure.

You've mentioned you run McAffee on all of your machines. Are the virus definitions kept up to date? If you have some suggestion as to particular machines behaving badly then you might want to run another vendor's antivirus on them to see if McAffee missed anything.

You probably also want to make sure you're not an open SMTP relay, though that normally isn't enough to get you listed with CBL.

share|improve this answer
    
Thanks for the help. I will try to address you comments, we only have a sharepoint intranet, no outward facing website, it is hosted by a 3rd party. We do have a FW policy to restrict all smtp traffic from the network from going out execpt for from our exchange server on port 25. Our virus def. are up to day within about 6 hours. I don't believe we are an open rely according to exchange settings online reports. Our firewall provide has spent a fair amount of time looking through our FW logs the last 2 days and hasn't found any thing. –  PBK Jul 2 '10 at 18:30
    
I have posted part of an smtp log. We use mxlogic as a mail filtering service for incoming mail. –  PBK Jul 2 '10 at 18:49
add comment
up vote 0 down vote accepted

It took a few days but we believe we have finally resolved the problem. It turns out that when our firewall was replaced the new configuration was sending out reports outside of our network and then back in, instead of just internally. This wouldn’t have been an issue if the email relay in the firewall was setup with a FQDN but it was actually seen as a generic ip of 127.0.0.1 which was then being picked up as possible spam. So several days of trouble shooting was the result of just one misconfigured email going out at midnight each night.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.