SBS08 | Disk Space / Exchange / “Back Pressure” Thought Process & Resolution

It all started off with this problem, after being all scatty and trying to get my head around the issue I thought I’d need to document this, hopefully to give a better sequence of debugging the issue rather than the mad chicken running round with no head!…


  • Internal Email all working
  • External Email outbound all working
  • No Inbound Email but no NDR from recipients.


  1. MX Lookup Confirm where the mail goes to?
  2. SMTP check Confirm the status of the server?
  3. Telnet: CMD -> “telnet 25” Also another method to provide some different information and confirm if this server is answering requests for the inbound email…
  4. Server check Disk Space: This is one of the most likely causes I have seen with server problems causing a raft of issues. But was thrown by 4GB free (Assuming this would be enough)
  5. Check Event Viewer: Ahh… the log of knowledge! well not quite if it doesn’t show anything obvious… At first glance this didn’t hi-light any problems but looking further I was given this to work with: “Exchange Server 2007 Transport: 452 4.3.1 Insufficient system resources”
  6. Google check: With something to go on I can do a little bit of Googling. To be fair I’m sure that’s what we all do for a new problem!
  7. Cause Identified:


  • The “Back Pressure” feature has kicked in and is not accepting requests.
  • The problem is the 4GB DISK SPACE!!


  1. Free Disk Space: The link above shows the tweaks and how to turn off “Back Pressure” but this can be avoided by simple cleaning up the disk space on C:\ and restarting the “Exchange Transport” service.
  2. Where is Disk Spaced used? Download Jamsoft Treesize, to show what space on c:\ has been consumed.
  3. How can I free up disk space on Windows Small Business Server 2008? – Being new to SBS as I usually work with Server 2008 STD/ENT I needed to confirm what can be cleaned up. Cleanup: IIS log files seem to waste a lot of disk space. The following script taken from: will clean them up.

@echo off
rem Script to clean up disk space on SBS 2008 servers
rem Downloaded from
rem V1.0 – March 28th, 2010

rem Certificate Services Logs
net stop “Active Directory Certificate Services”

del c:\windows\system32\certlog\*.log
del c:\windows\system32\certlog\*.chk
del c:\windows\system32\certlof\*.jrs
net start “Active Directory Certificate Services”

rem IIS Log Files
Del C:\inetpub\logs\LogFiles\*.log /f /s


Once the disk space issue was addressed we could then restart the “Exchange Transport” service. This then kicked Exchange back into life, although it didn’t comeback up instantly! And the service was restarted a few times for it to register (not sure the reason for this)

Although this has resolved the problem for now, we will need to move the Exchange DB off the C:\ (not sure why there in the first place) so this doesn’t become an issue again…

Move the Exchange Server Data

Links which helped (Thank you)

1 thought on “SBS08 | Disk Space / Exchange / “Back Pressure” Thought Process & Resolution

  1. MxToolBox

    Thanks for recommending our tools in your process of identifying issues with the Backpressure feature. I wanted to mention that our tools can also alert you if your server is having a problem via email or text:

    We also have an article about the Backpressure feature as well if you wanted to reference it:


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