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Unable receive email from remote Mail server through Lan-to-Lan VPN although tunnel is established

Posted on 2007-12-03
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Last Modified: 2013-11-30
VPN tunnel is up and I can successfully send email to remote mail server, just not recieve email from them. Their mail server says that they have successfully sent email, but I never receive it. I've enabled SMTP logging, but don't show any incoming connections from that server. There are however entries in the log occuring every 10 seconds:

19:13:36 172.25.10.143 QUIT - 240
19:13:46 172.25.10.143 QUIT - 240
19:13:56 172.25.10.143 QUIT - 240
19:14:06 172.25.10.143 QUIT - 240
19:14:16 172.25.10.143 QUIT - 240
19:14:16 172.25.10.143 QUIT - 240

I've installed a sniffer on my mail server and can see several smtp handshack attempts between the two mail servers, but no mail connections are ever established.

x.x.x.254        x.x.x.141         TCP      56860 > smtp [SYN] Seq=0 Ack=0 Win=49640 Len=0 MSS=1380
 x.x.x.141         x.x.x.254         TCP      smtp > 56860 [SYN, ACK] Seq=0 Ack=1 Win=16384 Len=0 MSS=1460
x.x.x.254         x.x.x.141          TCP      56860 > smtp [ACK] Seq=1 Ack=1 Win=49680 Len=0
 x.x.x.141          x.x.x.254        TCP      smtp > 56860 [FIN, ACK] Seq=1 Ack=1 Win=16560 Len=0
x.x.x.254          x.x.x.141          TCP      56860 > smtp [ACK] Seq=1 Ack=2 Win=49680 Len=0
x.x.x.254          x.x.x.141          TCP      56860 > smtp [FIN, ACK] Seq=1 Ack=2 Win=49680 Len=0

I've changed the smtp debug level to 7, but still don't see anything coming in.

Any other suggestions?

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Question by:cogentsystems
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11 Comments
 
LVL 21

Expert Comment

by:from_exp
ID: 20401255
Hi there!
19:13:36 172.25.10.143 QUIT - 240
19:13:46 172.25.10.143 QUIT - 240
19:13:56 172.25.10.143 QUIT - 240
19:14:06 172.25.10.143 QUIT - 240
19:14:16 172.25.10.143 QUIT - 240
19:14:16 172.25.10.143 QUIT - 240
it means someone is trying to contact imap servise on your mail server. I don't know what does mean 240 however

x.x.x.254        x.x.x.141         TCP      56860 > smtp [SYN] Seq=0 Ack=0 Win=49640 Len=0 MSS=1380
 x.x.x.141         x.x.x.254         TCP      smtp > 56860 [SYN, ACK] Seq=0 Ack=1 Win=16384 Len=0 MSS=1460
x.x.x.254         x.x.x.141          TCP      56860 > smtp [ACK] Seq=1 Ack=1 Win=49680 Len=0
 x.x.x.141          x.x.x.254        TCP      smtp > 56860 [FIN, ACK] Seq=1 Ack=1 Win=16560 Len=0
x.x.x.254          x.x.x.141          TCP      56860 > smtp [ACK] Seq=1 Ack=2 Win=49680 Len=0
x.x.x.254          x.x.x.141          TCP      56860 > smtp [FIN, ACK] Seq=1 Ack=2 Win=49680 Len=0

what is your mail server ip 141 or 254?
if 141 - then stmp session from the remote mail server can be established
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Author Comment

by:cogentsystems
ID: 20404985
IMAP is disabled. We're only using POP3 and SMTP services.

Our IP is 141.

I can see the sequence SYN, SYN/ACK, ACK, but there is no SMTP Response that opens the connection to send the email commands through. My mail server just closes the connection by responding back with a  FIN/ACK.

I can't figure out why my Exchange server is denying their connection. Is there any other debugging levels that I can change to get more information?
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LVL 21

Expert Comment

by:from_exp
ID: 20405309
strange...
i'm not an expert with Exchange, but what about receiving e-mails from other mail servers?
what event log messages does exchange generate?
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Author Comment

by:cogentsystems
ID: 20405332
I can receive from other mail servers fine. No event log messages related to this.
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LVL 21

Expert Comment

by:from_exp
ID: 20405378
what about domains: what relations do you have between two servers ?
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Author Comment

by:cogentsystems
ID: 20406500
Separate domains.

I think I found out the problem. I have two network interfaces on separate subnets. The SMTP virtual server has an ip x.x.x.147 on LAC#1. LAC#2 is on a different subnet and is connected to the remote server I'm having issues with via the VPN tunnel. I've setup an SMTP connector to forward email destined for a different domain to be sent through the VPN tunnel over LAC#2. Response emails are supposed to come back through the VPN on LAC#2. The problem is that the SMTP Virtual Server is only listening on LAC#1's IP, which is why it's denying all incoming connections from LAC#2 over port 25.

I have a Windows Cluster, but can't figure out how to create another SMTP virtual server resource, or set the IP to "All Unassigned".
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LVL 21

Expert Comment

by:from_exp
ID: 20406565
nice,
about exchange, if i remember correctly:
exchange mmc console, server - protocols - snmtp - default smtp virtual server - all assigned in the general tab
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Author Comment

by:cogentsystems
ID: 20407014
It won't let me chance it since it's in an Exchange Cluster.
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LVL 21

Accepted Solution

by:
from_exp earned 500 total points
ID: 20407032
hm, I'm not an exp in clustering, but one of the boxes is master, second is slave from the configuration point of view.
you should be able to change it on master box.
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Author Comment

by:cogentsystems
ID: 21206197
Problem solved
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Author Closing Comment

by:cogentsystems
ID: 31412441
Thanks for the help.
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