Now, I'm a complete n00b to Outlook 2007 administration, but after deleting a whole bunch (thousands? more?) of automated alerts, I decided to try a more immediate solution to tame my 2.2GB inbox PST. My first course of action was to compact the PST, via the Data File Management dialog and clicking on "Compact Now" for the correct inbox.

This may have been mistake #1 (perhaps the only mistake), but after a period of about 30 minutes, I hit 'Cancel' and figured I'd wait until the end of the workday. By this point, the size on disk of that inbox' PST was 3.2GB. Uh oh. Any subsequent attempts to compact the file have taken about 10 seconds to process, and not much happens. I've been checking activity via FileMonitor, but there are only a handful of reads, writes, and flushes to the PST, and the file size remains the same.

Finally, I tried forcing an archive of the inbox, and while my Archive.pst grew by about 500MB (I rarely archive, and don't have autoarchive on), Outlook.pst will not budge in size.

Any thoughts as to what I can do, or at least what I did wrong (feel free to chide me!)?

Edit: I'm not sure if it's relevant, but this is just against a POP3 server, not Exchange.

Edit^2: So I ran ScanPST in Program Files\Microsoft Office\Office12, and it did find errors that required attention...but the net result is that, without Outlook running (and thus receiving more mail), the PST file grew another 100MB.

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    Don't cancel compacting a PST. Next time this happens-- and it will happen again-- set the PST to compact overnight and just let it do its thing. – davidcl Feb 14 '10 at 12:31

Basically put, you could create a new PST file and manually drag and drop everything over into it. This would then be set as your new delivery file and the old rather chunky PST file would be closed/deleted.

  1. Firstly, either disable sending and receiving in Outlook or simply kill your internet connection temporarily. This will prevent new emails going into the old PST file and vanishing during the move process.

    I would recommend using the right-mouse button to drag and drop, selecting Copy instead of Move. That way, you can backtrack if anything goes wrong at any point.

  2. Ensure you are in the Folders view so that you can see everything including contacts, calendar, etc etc. Drag and drop everything across into the new PST file. Once you are sure that everything is in the new PST, close Outlook.

  3. Open the Mail applet from Control Panel and change the mail delivery to point to the new PST file.

  4. Open Outlook and close the old PST file from the left-hand side of Outlook by right-clicking it.

As for the why, I would also be interested to know. My initial stab in the dark is that the compress function is similar to defragmenting a disk. Chunks of the PST file are reordered in such a way that they are all contiguous, thus removing the gaps due to deleted emails, etc, making the overall size of the PST file smaller. My guess is that all the chunks were moved beyond the original size of the PST file, ready to be copied back in the right order without the gaps... right before the process was cancelled. I am sure someone will be more than happy to correct me if I am completely wrong!

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  • Yep. Hate it, but big PST files just get corrupted sometimes and you have to do this occasionally. – davidcl Feb 14 '10 at 12:30

PST files sometimes get wacky when they get over 2GB.

You might want to run Outlook's ScanPST utility (usually located in C:\Program Files\Microsoft Office\Office12 for Office 2007) against it and see if that helps out.

Here's some good info on how to use it.


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Something you may want to consider for automatic alert emails is to set a custom rule to move them to a folder. Then you can auto-archive that folder, but instead of moving them, choose delete and a sufficient retention period. No longer will your PST be filled with useless alerts.

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  • You can actually set a rule to move them to a different PST file from the one that contains your normal mail. This is what I do. – davidcl Feb 14 '10 at 12:29
  • Nice, never even thought of that. In my case all my automated emails are worthless after a day or two so why keep them. But I can definitely see some use for moving to a different PST. – Fishwalker Feb 15 '10 at 15:28

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