Exchange 2007 / 2010 Inbound Mail-flow Suddenly Stops – Quick Fix

What is Backpressure?
Backpressure is a new ‘feature’ in Exchange 2007 / 2010 where Exchange actually monitors resources such as Free Disk Space on the disk where the Exchange Message Queue / Message Queue Transaction Logs live and the Memory that the Edgetransport.exe process is using and memory in general used by other processes.

How do I know if my server is suffering from Backpressure?
If one or more items being monitored hits pre-defined limit, then Exchange will stop inbound mail-flow, so usually the first thing that you notice is that all of a sudden, you are not receiving emails from the rest of the world. You will be able to continue to send emails, you just won’t receive and new emails.

Look in your event logs and if Backpressure is being applied, you will see Event ID’s 15006 or 15007 in the logs:

Event log entry for critically low available disk space
Event Type: Error
Event Source: MSExchangeTransport
Event Category: Resource Manager
Event ID: 15006
Description: The Microsoft Exchange Transport service is rejecting messages because available disk space is below the configured threshold. Administrative action may be required to free disk space for the service to continue operations.

Event log entry for critically low available memory
Event Type: Error
Event Source: MSExchangeTransport
Event Category: Resource Manager
Event ID: 15007
Description: The Microsoft Exchange Transport service is rejecting message submissions because the service continues to consume more memory than the configured threshold. This may require that this service be restarted to continue normal operation.

How do I get mail-flow restored quickly?
For a quick fix, modify the edgetransport.exe.config file (notepad works happily for this) found in c:\program files\microsoft\exchange server\bin (Exchange 2007) or c:\program files\microsoft\exchange server\v14\bin (Exchange 2010)

Search for and change the “EnableResourceMonitoring” from “True” to “False”, save and close the file, then restart the Microsoft Exchange Transport Service.

Okay – so mail-flow has been restored – what to do next?

Once your inbound mail-flow has returned (assuming disk space is an issue, which has been the case every time I have seen Backpressure applied), then tidy up your drives and if you are not backing up your Exchange Server (which will purge the Exchange Log files), then make sure you do!

Once you have tidied up your drives and freed up some disk space, set the “EnableResourceMonitoring” back to “True” in the edgetransport.exe.config file and then restart the Microsoft Exchange Transport service again.

Further reading:
Exchange 2007 – Microsoft Backpressure Article:

Exchange 2010 – Microsoft Backpressure Article:

Backing Up Exchange 2010 with Windows Backup:


25 Responses

  1. Works however I had to restart MS transport service in order for it to work I dint have an Edge Transport service

  2. You are a lifesaver!!!! Thank you so much for posting this. I was frantically trying to get e-mail back up for our office and came across this. Thank you so much!

    • How long will it take to see any messages that were received but not delivered?

      • Once backpressure kicks in, all inbound mailflow will stop, so nothing will be accepted. Any mail trying to make its way to your server will not be able to be sent, so there is nothing received and not delivered.

        As soon as you have removed the backpressure status, mailflow will return to normal and the sending servers waiting to retry sending to your server should be able to deliver the email on the next connection attempt, whenever the sending server is scheduled to retry.

        As such, you won’t see any emais timestamped during the backpressure period because your server stamps the emails upon receipt and it hasn’t received then.

        Once backpressure is gone, mail will be received and timestamped showing the time of receipt and Outlook will show a gap. If you are down for 1 hour before fixing the problem, Outlook will show an hours gap between the last email received before backpressure kicked in and the time that you fixed the problem.

        Hope that all makes sense.


  3. Any thoughts as to why it says “cannot create the (directory). Make sure that the path and file name are correct.” ??

  4. Thanks for the quick response. More details would help, huh? I was trying to modify the .config file and save it. Apparently, the Domain Admin I was logged in as did not have sufficient rights. Once I logged in as THE Administrator, the config file that I modified was able to be saved properly.

  5. How do you guys know all these man? Many thanks – Mail flow working fine now. I won’t forget this error in my life again.

  6. Alan – You’ve helped me before on I’m having the issue with Edge Transport Service stopping. I’ve changed the config file to false and we have over 300GB of free space. I’ve followed everything I find on the internet but nothing is working. We haven’t received email for the last two days. Is there something else to check?


  7. Alan, thank you so much for this. Just a couple of things to add: I had to change permissions on the bin directory as it was read only, and I found that the WSUS database and files had filled up my C drive, which is fairly common and well documented:

    Thanks once again for taking the time to share this with the internet community.

  8. Alan you’re a LIFESAVER! Thank you!!!

  9. Hello, thanks for this wonderful advice. I noticed your comments to Nat above about the servers resending the mail, however its been a couple of days since we did this, and it seems about 100 or so emails never arrived. I sent several test messages from my server which were never received. I checked exchange queues from my server and there are no emails in there waiting to resend. I think that during the time the server was not delivering mail, it was accepting it from the edge transport service, but not delivering them. Could those messages still be in the old location? by the way, this client also uses mxlogic which is supposed to spool messages when the server is down, however according to them, the server never went down. These emails are critical to my client and could cost them a million dollar bid. HELP!!

    • Hi Justin,

      How long did you have a problem for before it was fixed (if you know)?

      As your mail would have been accepted by the Edge Transport server, it would have tried to pass it to the CAS server but may have timed out and sent back an NDR to the sender when it couldn’t deliver it in time.

      Outbound mail does not normally get affected by backpressure unless it reaches the High setting, so I doubt mail not being received is related. If you did reach the High setting, then mail would not go out, but it wiuld still be queued and keep retrying until it either sends the message or it times out. You should also get delayed delivery messages if it is queued for any length of time.


  10. Thanks for your article, I was very useful. Do you know how to purge the Exchange Log files safely?

  11. is there a hard percentage that the backpressure kicks in at? like 5% or 3% of remaining free space? I’m trying to set some alarms for myself prior.

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