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Intermittent Queuing of Outbound SMTP Messages

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Intermittent Queuing of Outbound SMTP Messages - 23.Apr.2007 1:30:08 PM   


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Joined: 23.Apr.2007
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We have one Exchange 2003 server that services about 300 users.  Mail addressed to recipients outside our organization is forwarded using the Default SMTP connector to a Postfix server in a DMZ which acts as an MTA. This configuration has worked fine for the better part of a year . Recently we installed DoubleTake replication software on the Exchange server to replicate the mail to a DR site. This replication process has been in place for two or three months with no issues.

A  week ago, outbound mail started queuing in the Default SMTP connector queue. Inbound mail was still functioning fine (routed in through the same Postfix gateway), as was all internal mail. I was able to force a connection in System Manager and get the mail to start flowing again. Mail would be sent out fine for about an hour or so and then start queuing up again. Sometime that evening I bounced the Exchange server and once it was back up, everything worked fine through the night and into the next day. Since that day, Exchange runs fine all day, until around 8pm, when mail starts to queue again in the Default SMTP Connector queue. I can usually force the connection one time and mail will flow, but only for about 20 minutes. After that it will start to queue up again. At this point I can no longer force a connection and must reboot the server. Once it comes back up outbound mail flows fine until the next night when the problem reoccurs. One thing I noticed was that outbound mail was starting to queue within minutes of our nightly NetBackup Exchange backup. This backup has been running since the server was built without any issues. I put the backup on hold Friday night and outbound mail stayed up longer, but eventually started queuing up around 1:30am so about  5 hours later than it had been the previous nights when the backup was running. I'm thinking that the backup is exacerbating whatever the issue is, which is in turn causing the mail to start to queue.

Some other observations:

- The server is a dual-core 2.4 GHz AMD with 4GB RAM and an attached disk array. There are currently no disk space issues.
- The Exchange server is running Windows 2003 SP2, which I installed after the problem started. All other patches are up-to-date.
- There are no errors in any of the event logs that indicate a problem.
- I have changed the Exchange SMTP Default Connector to route mail through a completely different MTA that is also in the DMZ to rule out a Postfix issue. The same problem occurs when routed through this MTA.
- I paused the DoubleTake replication and mirroring a day or two after the problems started without any noticeable effect.
- When mail starts to queue and I highlight the queue in System Manager, it says something under Additional queue information like: The network host is no longer available. When I try to telnet to the Postfix server from the Exchange server at this point, it times out. When outbound mail is not queuing, I can telnet to the server without any issues.
- I have run the Exchange Performance Monitor on the server when the mail starts queuing and it returns errors about RPC latencies and disk bottlenecks. 
- When outbound mail is flowing fine and I run PerfMon, non of the aforementioned errors show up.
- A remote office in Asia is coming online around 8pm and connecting to the Exchange server here through Riverbed Steelhead WAN Optimizers. The Steelheads are doing some MAPI optimization, acceleration and prepopulation for these users. This has been in place for about two months without any known issues.
- Again, inbound mail (from outside) and internal mail experience no problems during the times when external outbound mail starts queuing.

Any help would be greatly appreciated. Thanks.

< Message edited by afiore -- 23.Apr.2007 1:31:55 PM >
Post #: 1
RE: Intermittent Queuing of Outbound SMTP Messages - 23.Apr.2007 2:38:23 PM   


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Joined: 1.Dec.2005
From: Centreville, Virginia
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When it starts queueing up, you cannot telne to the postfix server, can you telnet to any other server?

James Chong (MVP)
MCSE | M+, S+, MCTS, Security+

(in reply to afiore)
Post #: 2
RE: Intermittent Queuing of Outbound SMTP Messages - 23.Apr.2007 3:02:19 PM   


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Joined: 23.Apr.2007
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I cannot telnet to the other MTA that I mentioned that is also in the DMZ. However, we do have another SMTP relay inside the firewall that we use for internal SMTP messages that I have not attempted to telnet to when mail starts queuing up. Other network communications (i.e. http traffic to the web) seems unaffected.

(in reply to jchong)
Post #: 3
RE: Intermittent Queuing of Outbound SMTP Messages - 23.Apr.2007 3:55:09 PM   


Posts: 8232
Joined: 7.Jan.2004
From: California, USA
Status: offline
Sorry for crashing the party late, but I have a couple of questions:

When the telnet session to the Postfix server times out - can you see the port 25 traffic pass through the firewall?  I'm wondering if you can tell if the communication drops from Exchange to the firewall or from the firewall to Postfix.

You paused the Doubletake replication (and not that this has anything to do with the issue), but is it configured to automatically failover?



Dean T. Uemura
Microsoft MVP - Exchange (2007-2011)

(in reply to afiore)
Post #: 4
RE: Intermittent Queuing of Outbound SMTP Messages - 24.Apr.2007 1:28:34 PM   


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Joined: 23.Apr.2007
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Thanks for the help. We actually figured it out. Apparently WebSense pushed an update that changed the way that SMTP is monitored. With this change, the rule allowing Exchange to pass SMTP messages to the DMZ worked fine, until a user logged into the Exchange server - be it on the console or as a service (i.e the NetBackup service account). When a user logged in, Websense stopped processing the Exchange server traffic by IP and started processing it by user. The IP was allowed to send SMTP, all the various users were not.

(in reply to afiore)
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Posts: 12
Joined: 22.May2007
Status: offline
I have contacts from foreign domain in my AD forest domain that I want to import into my exchange 2003 organisation GAL. How can I achieve this process thru VBscripting.

(in reply to afiore)
Post #: 6

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