Cannot Receive Internet Mail with Exchange 2007

I ran into a very interesting issue with our company’s internal Exchange 2007 server. When we originally deployed Exchange 2007, there were a number of dependent programs that were not available for Exchange 2007. One of these was disclaimer program as well as an internal ticket tracking and accounting system. Several months after the original implementation these programs released updates to their products and were certified to run on Exchange 2007.

After hours we began the process of migrating these applications to the new Exchange 2007 server and decommissioning the old Exchange 2003 server. The send connector and receive connectors were modified so that the Exchange 2007 server was internet facing and also the primary server for sending outgoing mail.

Once these changes were made inbound, outbound, and internal emails were sent to test the configuration. All returned results and there were no issues. We then began working on moving the previously Exchange 2003 dependent programs to Exchange 2007. After an hour or so, we noticed that external email was no longer received by the Exchange 2007 server.

No changes had been made to the email routing configuration since the initial changes were made an hour earlier. Outbound email and internal mail messages were successfully sent and received. Only mail from the Internet was not received.

After reviewing my receive connectors on the Exchange 2007 server I then performed a telnet to the Exchange box using my external email address. One of the messages I received after the “MAIL FROM:” line was “4.3.1 Insufficient System Resources in Exchange Server 2007”

Odd… The server was not under a heavy load and had recently been rebooted. I then began looking deeper and into the Event logs. What I found was the event below which is pretty cryptic without additional resources and explanations.

Event Type: Warning
Event Source: MSExchangeTransport
Event Category: ResourceManager
Event ID: 15002
Date: 01/01/2007
Time: 12:00:00 PM
User: N/A
Computer: EXCHANGE
Description:
The resource pressure is constant at MediumHigh. Statistics:

Queue database and disk space ("C:\Program Files\Microsoft\Exchange Server\TransportRoles\data\Queue\mail.que") = 77% [MediumHigh] [Normal=75% MediumHigh=77% High=79%]

Queue database logging disk space ("C:\Program Files\Microsoft\Exchange Server\TransportRoles\data\Queue\") = 77% [Normal] [Normal=93% MediumHigh=95% High=97%]

Version buckets = 3 [Normal] [Normal=40 MediumHigh=60 High=100]

Private bytes = 4% [Normal] [Normal=71% MediumHigh=73% High=75%]

Physical memory load = 56% [limit is 94% to start dehydrating messages.]


Inbound mail submission from the Internet, the Pickup directory, and the Replay directory has stopped.
Loading of e-mail from the queuing database, if available, continues.


For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.

The key to deciphering this event is the values associated with each threshold. Above it states that “The resource pressure is constant at MediumHigh” and meets the following thresholds: Queue database and disk space & Queue database logging disk space. These are both located on the C: drive.

In this particular instance, the C: partition on the server was roughly 20GB in size and there was about 4.5GB of free space. Looks like plenty, right? To define the behavior of each threshold when it is met, refer to the following definitions.

· Normal - The resource is not overused. The server accepts new connections and messages.
· Medium - The resource is slightly overused. Back pressure is applied to the server in a limited manner. Mail from senders in the authoritative domain can flow. However, the server rejects new connections and messages from other sources.
· High - The resource is severely overused. Full back pressure is applied. All message flow stops, and the server rejects all new connections and messages.

Since the queue database and logging both reside on the C: drive of this particular Exchange 2007 server we met the first two thresholds at “MediumHigh”. This level allows mails to flow internally and outbound, but rejects Internet mail.

Initially I removed some unnecessary IIS logs and before the delete operation had completed I began to see emails flow into my Inbox. Sure enough, Exchange 2007 had stopped functioning due to “low disk space” with over 4GB free on the drive!

So, how can we tell Exchange 2007 to allocate and use the additional space on the C: drive? This can be done by modifying the EdgeTransport.exe.config file found in the “C:\Program Files\Microsoft\Exchange Server\Bin” directory

Most values are given in percentages, but for guidance refer to the following link provided by Microsoft (http://technet.microsoft.com/en-us/library/bb201658.aspx) Below is an example of the changes made to our EdgeTransport.exe.config file.

add key="PercentageDatabaseDiskSpaceUsedHighThreshold" value="95"
add key="PercentageDatabaseDiskSpaceUsedMediumThreshold" value="92"
add key="PercentageDatabaseDiskSpaceUsedNormalThreshold" value="90"
add key="PercentageDatabaseLoggingDiskSpaceUsedHighThreshold" value="95"
add key="PercentageDatabaseLoggingDiskSpaceUsedMediumThreshold" value="92"
add key="PercentageDatabaseLoggingDiskSpaceUsedNormalThreshold" value="90"

Essentially, I changed the “Back Pressure” feature to not worry about disk space until more than 92% of the disk is consumed. The default value of 75% is unusually low to me and I feel that a value of 90% and above should give an Administrator plenty of time to make corrections to their Exchange 2007 server to avoid an unplanned outage. To be safe, restart the “Microsoft Exchange Transport” to ensure the new config file is loaded and used.

So, now you know about the unfortunate truth of “Back Pressure” and its standard out-of-the-box default values. Back Pressure still serves a good purpose, but without the proper tuning you can find yourself scrambling to get your email server up and running again when nothing is really even wrong.