An Exchange Server 2007 server may stop processing mail and begin logging errors when the disk volume used for the Exchange Transport queue database becomes low on free disk space.

For even more detail on this topic please read A Guide to Back Pressure in Microsoft Exchange Server.

There are two key indicators of the issue:

Event ID 15002 or 15003 logged to the Application event log

Event Type: Warning
Event Source: MSExchangeTransport
Event Category: ResourceManager
Event ID: 15002
Date: 24/07/2007
Time: 1:40:03 PM
User: N/A
Computer: TESTEXC1

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”) = 64% [MediumHigh] [Normal=61% MediumHigh=63% High=65%]

Queue database logging disk space (“C:\Program Files\Microsoft\Exchange Server\TransportRoles\data\Queue\”) = 64% [Normal] [Normal=91% MediumHigh=93% High=95%]

Version buckets = 1 [Normal] [Normal=40 MediumHigh=60 High=100]

Private bytes = 21% [Normal] [Normal=71% MediumHigh=73% High=75%]

Physical memory load = 64% [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.

Inbound internet mail is not received and external messaging systems report SMTP error “4.3.1 Insufficient system resources” when connecting to your Edge Transport or Hub Transport servers

220 TESTEXC1.testing.local Microsoft ESMTP MAIL Service ready at
Tue, 24 Jul 2007 13:47:21 +1000
helo
250 TESTEXC1.testing.local Hello [10.1.1.11]
mail from: test@test.com
452 4.3.1 Insufficient system resources

The cause of this issue is free disk space falling below the normal threshold for the disk volume used by the Exchange Transport queue database.  Free disk space for the Exchange Transport queue database is one of the resources monitored by the Exchange Server 2007 “Back pressure” feature.  You can read a very detailed description of this feature here.

The “medium” pressure threshold is calculated by a formula as follows:

100*(hard disk drive size – 4 GB) / hard disk drive size

So for example, a 16Gb volume will have a “medium” pressure threshold of:

100*(16 – 4) / 16 = 75%

At “medium” pressure internal mail flow will still occur, however inbound internet email will not be received and any applications that use non-MAPI methods to send email (eg they use the Pickup queue) will also cease being able to send email.  Anything under 4Gb of free space is automatically considered “high” pressure, which ceases all mail flow.  These thresholds are configurable so that instead of relying on the formula you can hardcode the percentage values that you would like, however I don’t recommend this and I am leaving it outside the scope of this particular blog post.

However a solution I do recommend is to relocate the Exchange Transport queue database to another volume.  By default the database is installed to the same location as the Exchange Server 2007 program files.  For some deployments this means the C: drive, along with the operating system and other application files.  With Exchange Server 2003 it was a simple enough task to relocate the MTA queue to a different volume (often a dedicated volume).  The MTA would also operate quite happily as long as it had at least 10mb of free disk space.  The new Exchange Transport queue database will by default require more than 4Gb of disk space, and you would size this volume according to your organisation’s requirements.

Exchange Server 2007 has a limited administrative GUI.  Most simple tasks are enabled in the GUI, but more advanced tasks are only available via the Exchange Management Shell (PowerShell).  Moving the Exchange Transport queue database is not even available in the shell – you need to directly edit a configuration file to make this change.

The config file is the EdgeTransport.exe.config file, located in the \bin folder of your Exchange Server 2007 program files installation (eg C:\Program Files\Microsoft\Exchange Server\bin).  By default this would mean the location of the queue database is “C:\Program Files\Microsoft\Exchange Server\TransportRoles\data\Queue”.

Open up the config file and look for these entries:

<add key=”QueueDatabasePath” value = “…” />
<add key=”QueueDatabaseLoggingPath” value = “…” />

Change the path to the new location where you would like to store the database.  Exchange will automatically create the new folder if it does not already exist, provided that the drive or parent folder has the correct permissions already.  These are:

  • Administrators – Full Control
  • System – Full Control
  • Network Service – Full Control

You can also manually create the new location yourself.

If you are planning to just relocate the database without copying the existing database, then simply edit and save the file, and then restart the Microsoft Exchange Transport service.  If you want to retain the existing queue database, then you need to manually copy or move the files yourself, edit and save the file, and then restart the service.

If you have performed these tasks correctly and the new volume has adequate free disk space then the Exchange Transport agent will resume normal email processing.

About the Author

Paul Cunningham

Paul is a former Microsoft MVP for Office Apps and Services. He works as a consultant, writer, and trainer specializing in Office 365 and Exchange Server. Paul no longer writes for Practical365.com.

Comments

  1. Randy

    All of these articles have saved me a lot of heheacads.

  2. Kevin Williams

    Exchange 2013 SP1 CU5

    I am getting this back-pressure event (452 4.3.1 Insufficient system resources) and inbound (external) email is being delayed.

    Both my system (C:) and data (D:) drive have well over 60GB free disk space – yet I keep getting this message.

    Any help on where I should look to disable or correct this issue?

    Thanks!

    1. Paul Cunningham

      Back pressure isn’t only caused by low disk space. Event logs will record back pressure events.

      Some more info:
      https://www.practical365.com/exchange-transport-server-back-pressure/

      Also with Exchange 2013 make sure you’re looking at the correct server role. Transport is on the Mailbox server now, so if you’ve got separate server roles installed then you’ll need to look at your Mailbox not Client Access servers.

  3. Shah

    Hi Paul,

    Thank you very much for your guidance. I’m able to solve my problem yesterday.

  4. erlis

    We’re running an Exchange 2007 SP3 server with a C:-disk of only 23GB and approx. 1.5GB free storage, so we’ve run into this problem a few times, usually solved by a little cleanup and a reboot – but I really think it’s time to move the queue-database.

    My question however is regarding wheter or not I should move the database-files as well? We currently have mail.que of ~340MB and 5MB log/jrs-files in the queue-folder. What services do I need to turn off before being able to move these files, and what are the results of moving/not moving these files?

    Thanks in advance for your question, as well as an awesome article really comming in handy 🙂

  5. Sabu

    i have an issue with Exchange 2007 SP1, could you please helpme

    og Name: Application
    Source: MSExchangeTransport
    Date: 4/16/2012 3:23:32 PM
    Event ID: 15004
    Task Category: ResourceManager
    Level: Warning
    Keywords: Classic
    User: N/A
    Computer: exserver.domain.local
    Description:
    Resource pressure increased from Medium to High.

    Resource utilization of the following resources exceed the normal level:
    Version buckets = 233 [High] [Normal=80 Medium=120 High=200]

    Back pressure caused the following components to be disabled:
    Inbound mail submission from Hub Transport servers
    Inbound mail submission from the Internet
    Mail submission from the Pickup directory
    Mail submission from the Replay directory
    Mail submission from Mailbox servers
    Mail delivery to remote domains

    The following resources are in the normal state:
    Queue database and disk space (“H:Queuemail.que”) = 2% [Normal] [Normal=95% Medium=97% High=99%]
    Queue database logging disk space (“H:Queue”) = 2% [Normal] [Normal=95% Medium=97% High=99%]
    Private bytes = 3% [Normal] [Normal=71% Medium=73% High=75%]
    Physical memory load = 55% [limit is 94% before message dehydration occurs.]

    Event Xml:

    15004
    3
    15
    0x80000000000000

    906
    Application
    exserver.domain.local

    Medium
    High

    Resource utilization of the following resources exceed the normal level:
    Version buckets = 233 [High] [Normal=80 Medium=120 High=200]

    Back pressure caused the following components to be disabled:
    Inbound mail submission from Hub Transport servers
    Inbound mail submission from the Internet
    Mail submission from the Pickup directory
    Mail submission from the Replay directory
    Mail submission from Mailbox servers
    Mail delivery to remote domains

    The following resources are in the normal state:
    Queue database and disk space (“H:Queuemail.que”) = 2% [Normal] [Normal=95% Medium=97% High=99%]
    Queue database logging disk space (“H:Queue”) = 2% [Normal] [Normal=95% Medium=97% High=99%]
    Private bytes = 3% [Normal] [Normal=71% Medium=73% High=75%]
    Physical memory load = 55% [limit is 94% before message dehydration occurs.]

  6. Rajesh Boga

    My Hard Drive is 147 GB and I am facing Back pressure issue which states Low disk space issue, paul then how much free disk should be retained on disk to relive the issue. Secondly I have the only drive so moving queue database to other drive is not possible and also it is not recommended to disable the Back Pressure.

    1. Paul Cunningham

      It is really up to you how much you want to tune the back pressure thresholds.

      I’m a bit concerned that a 147Gb disk on an Exchange server is full though. What else do you have on that server taking up so much space?

      1. Rajesh Boga

        Paul my disk had free space of 5 GB but still I was facing issues with inbound mails from external domains, I moved all my data to other server. Now free space was more tha 90 GB.

        But how can I know, how much disk space should be retained on disk in future to keep away from problem.

      2. Paul Cunningham

        Rajesh, the default threshold is 4Gb. Or at least it was when I wrote this article. I haven’t checked since then to see if a later service pack changed it at all.

  7. Gary Tummond

    Fantastic! Thanks that was the exact problem.

  8. Paul Cunningham

    Shannon, the queue DB and folder can reside separately from everything else if you just want to make the changes in the post above.

  9. Shannon M

    Besides moving the Queue folder and files, do I need to relocate the other folders and files under the transportrole?

  10. Hans

    I really appreciate the info, I really do.

    Thanks a lot

  11. David

    Paul, You Rock! this is just what i needed. It worked just as you said it would.. Dinner’s On me Paul, Anytime!!!

  12. Alexander

    Thank you very much. This is exactly my case.

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