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How do i know what causes Outlook to slow down?

ksmirnov asked
hi, mighty all

recently My MS Outlook started getting irritatingly slow. I try to do my best in order to make the inbox small - offload old messages into archive, delete, empty the wastebasket.

My inbox is about 160 Megs, my Archive is 1,2 gigs. I keep it closed almots all the time. My PC has 2 GB of RAM, so swap is not an issue.

The symptoms are - when I repeteadly click on several messages, or several folders, Outlook gets stuck with CPU hitting up to 90%. Then, after 10-20 secs it gets back to normal.

I have several Outlook add-ins:
Agendus for Windows Outlook Edition by Iambic
Lookout (disabled)
Bells and Whistles by DS development
Kaspersky Antivirus
Cloudmark Desktop (Spam removing tool)

Even if I disable, say Kaspersky and Lookout - the most likeliest candidates, Outlook is still a drag. It seems like some indexing issue... but I can't really know for sure.

Is there any way to check - i.e. some Outlook performance tuning guidelines, some tools to check PST files integrity? Or maybe there is something completely different and I am looking at the wrong direction?

Thanks a million for your kind help.
Watch Question


Sounds like you have never compacted your Outlook storage file.

Try this:


Not really... did that just a week ago.
Wesley MillerComputer Network Analyst
You could use the Microsoft PST Compact Tool....
This utility is used as part of a specific process that attempts to recover data from a Microsoft Outlook data file (PST file) that is larger than 2 GB.  It is designed to be used under the supervision of a Microsoft support professional. To complete the recovery attempt, use the Inbox Repair Tool (scanpst.exe) on the PST file generated by this utility. Make sure to keep a backup of your original .pst file before using this tool.

To run it to just refresh indexes ,ect and not purge any data yuo have to add -s to the PST2GB.exe ie

Wesley MillerComputer Network Analyst

Okay, I guess you need the source for the tool!
Try going here for the Info on it:
here to Donwload it:



Isn't it for Outlook 2000? I tried to run it on my outlook.pst file, but the resulting file was unreadable by Outlook. I.e. I started it with PST2GB.exe -s, chose the source and destination files, it all went through, I saved the original file under the different name, renamed the resulting file "outlook.pst", started Outlook.

The Outlook says something like "the file is unreadable, due to being in a different format".
Am I missing something?

Oh, you should have said Outlook 2000 from the start.

Outlook 2000 didn't have support for local cache of your mailbox (for Native Exchange not POP).  So all mail functions such as reading your messages or simply viewing your inbox content is streamed traffic straight from exchange.

My biggest recommendation is to switch to an Outlook version that supports Cached Mode or the sync of only Headers on slow connections (Outlook 2003-2007).  That way Outlook can reference the local drive for email located in the main Exchange Mailbox.

Alternatively, disable preview features that makes server interpret the content of several emails, such as the Reading Pane, and Autopreview.

Cached Mode does wonders for Outlook performance.
I meant to include above, mailboxes over 100MB in size have noticeable latency issues with Outlook clients not working in cached mode.

You have to keep in mind that everything travels through the network in that scenario and your server is working for everyone.  Best to reduce its traffic load with a local cache.


gambit_642, actually my message was tagged as "Microsoft, Outlook, 2003, SP3". Sorry :-)

I have to aplogise for incorrectly stating the size of my main PST file size. It was 300 megs.

Here is what I have done - ran pstscan on my outlook file. It somehow helped. PSTSCAN.EXE found some broken references within my PST file. However, after I fixed PST file, its size grew nearly 50% in size and went to horrific 402 Megs!!! Aaargh...

I compacted it and it went to mere 320 Megs again...

So the resume is as follows:
1) PST2GB did not help me, however it gave me a hint to switch my attention to SCANPST (thanks, wmiller)
2) SCANPST did help a little, but just a tad
3) gambit_642 gave me a hint that I have to sharply decrease my inbox size
4) I hope that I will give my inbox reduction program a go over the weekend
5) after that I will close the question and allocate the points between wmiller and gambit_642

My best regards,


Neither of the solutions helped me 100%, but I certainly gained some speed increase.

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