Why Outlook 2007 is slow: Microsoft’s official answer

A knowledgebase article published last week acknowledges performance problems with Outlook 2007, though it says these only occur with mailboxes larger than 2GB:

You may experience one or more of the following performance problems when you are working with items in a large Personal Folder file (.pst) or in a large Offline Folder file (.ost) in Microsoft Office Outlook 2007 … Note When you perform the same operations on the large .pst or .ost file in earlier versions of Outlook, the same performance problems do not occur. These problems may occur if the .pst or .ost file is larger than 2 GB. Additionally, the performance problems are more pronounced when the .pst or .ost file is larger than 4 GB.

I think this is optimistic and that smaller mailboxes are slower too; nevertheless, it does confirm that that the size of the local store is the key issue.

If you use Exchange, the local store is the .PST or .OST file on your workstation or laptop. If you do not use Exchange, a local .PST store is all you have.

Here’s what Microsoft says is the reason:

To accommodate new features, Outlook 2007 introduced a new data structure for .pst and .ost files. In this new data structure, the frequency of writing data to the hard disk increases as the number of items in the .pst or .ost files increases.

Intriguing, especially as I had thought the .pst format was the same in Outlook 2003 and 2007. The big change was from Outlook 2000 to Outlook 2003, when Unicode was introduced and the maximum size increased to 20GB.

I’d also like to know whether Microsoft is just stating the obvious here (bigger file, more disk access); or whether there is some exponential increase in disk writes, suggesting a design fault in the software. I have already noticed that if you show the I/O columns in Task Manager’s performance tab, Outlook 2007 shows some extraordinarily large numbers.

So what’s the fix? The news is not too good. In essence, you have to reduce the size of the local store. You can archive or move items to separate .pst files, or switch off cached mode so you always work online to Exchange.

The article doesn’t say it, but there are significant problems with switching off cached mode. These include hugely increased network traffic, problems with junk mail filtering, and loss of all your mail when using a laptop disconnected from the network.

The most imaginative suggestion is to filter the sychronization. For example, you could filter out messagse with large attachments, or all messages from last year or earlier. These messages will still exist in Exchange, but not in the local store.

Worth a try, but none of the workarounds is really satisfactory. Outlook 2003 worked fine with large mailboxes, Outlook 2007 does not. That’s a blunder.


158 thoughts on “Why Outlook 2007 is slow: Microsoft’s official answer”

  1. OutLook 2007; It’s SLOW, but for me not particularly for the reasons others have stated here. The downloads are slow but as I only get 400-600 post a day. During downloads I’m busy on other errands. My complaint is mail viewing, each post takes tens of seconds to show in the view panel, when scanning dozens of posts, time is eaten rapidly. I’ve rarely had it crash on me but stalls are more or less common. My system is not old or slow and I more than less know my way around; AMD 64 – 3GHz, 2gb ram, 1.2Tb HD(s), MS XP Pro 64.
    I’ve implemented most useful hacks, but need insight for this viewing problem.

  2. HI guys,
    Do you know if there is an office 2007 uninstaller? one user connected his blackberry to outlook and synchronised his contacts, outlook copied down 1000 contacts and has been crawling since. I set the user up on outlook 2003 on another machine, synchronised all the contacts and it works perfectly. When I downgraded his original machine to 2003 it still kept the mailbox settings. Any ideas? Thanks.

  3. I owe it to the comments on this blog for saving my bacon with a client. Outlook 2007 was HORRENDOUSLY SLOW!! I mean click on an email header, wait 10 seconds, then the reading pane would populate. This went for EVERYTHING you clicked on in Outlook. Wait ten seconds……

    I checked processes and the DELL Media component was taking up 250megs of RAM. I killed the process and uninstalled the DELL Media component but things were still slow UNTIL I rebooted and then it was like having the new computer that it supposed to be (brand spanking new Inspiron Core2Duo, 2 gigs RAM running like a x286!!!)

    I going to report this to DELL.

  4. I have tried Outlook 2007 connected to the same Microsift Exchange Account on two Latops one running XP and one Vista. The Vista machine was OK but the XP machine was slow to the point of virtually freezing up completly although left for a few hours it seemed to recover eventually.

    Just took all the RSS feeds off and seemed much better. However wondering if it was the search indexing finishing indexing everything that actally cleared the problem.

    When the outlook was frozen the Task manager performance graph showed no activity at all.

  5. OOps! No seemed fine until next clicked to reply to a message then got the dreaded white screen area. Nice area of clean white screen set aside for the reply E Mail window but nothing there. “Not Responding” label on all the Outlook tasks. No activity on the processes at all. As if its waiting for something. It was in fact a complet permanent Outlook crash.

  6. Latest is that 1and1, who provide my Exchange server, tell me that I should not run Outlook 2007 on Windows XP as its is not compatable!? I should use Outlook 2003.

    Has anyone experiance running Outlook 2003 on XP successfully.

    1and1 provide a new Profile for Outlook 2007 but I have not figured out yet if its actually any different from the one for utlook 2003.

  7. I’ve had the same problem on several Dell Precisions in my Office, and I’ve tried all of the above mentioned fixes/patches.

    However, what worked for me was to turn off Exchange Auto-Protect in Symantec Antivirus (v 10.2)

    Outlook 2007 now back to being snappy and fast, despite a fairly large .OST file (1.3gb)

    Hope this may be of help to some of you.

  8. I have now tried absolutely everything to speed up 2007 and while it’s not quite as bad as it was, when I download pop email from my 5 accounts, it stops responding during the downloading every time. This is the most frustrating piece of software I’ve ever had!! Unfortunately there’s nothing else out there that has all of the features of outlook in 1!

  9. > Unfortunately there’s nothing else out there
    > that has all of the features of outlook in 1!

    Outlook 2003?


  10. Jelp,

    I have a brand new IBM Thinkpad T61 2.0Ghz Dual Core and frequentlyu like every 10 mins only havint Outlook 2007 open it grabs 100% of my CPU and just will not dosplay the drsaft files and keeps tellinmg me to close down other applications (by the way I am not running any pothers). Unfortunately my company is only using Vista Business and Outlook 2007. I dont think I have experienced such a situation with Outlook. This prodct is just hopeless. Can anyone suggest what I can do as basically I cannot work on my Notebook. I amdsolutely depend on Outlook. Surely Microisoft cannot be this incompetent with Outlook 2007.
    I have 3 old PST files admitted;ly one is 1,2GB, but my new PST file (or is it called an OST File is quoitre small with less than 50MB size, but this doesnt make any difference. What I dont understand is how with a Dual Core 2.0Ghz, 2GB RAM machine, Outlook 2007 can be so cripplngly slow.

    Can anyone suggest what I can do or another email client as a replacement?

  11. Hi!

    Thank you very much for keeping my System beeing kicked out of the window!

    Item No. 27 worked fine! Thank you so much!

  12. Solution to Slow Outlook is with Bazza posting #27.
    Bazza, you are a genius.
    I was about to throw my new lenovo out the window because of grindingly slow outlook.
    The command promt solution solved it INSTANTLY. I wish I had found your posting weeks ago.
    May good things come your way.

  13. viewing emails in Outlook 2007 (Vista, Dell Inspiron 6400, 2GB RAM) often took 20 seconds or more to view. The reading pane (view, reading pen) worked for a couple of emails then refused to work at all.

    I uninstalled Dell MediaDirect (allows playing of audio/video without booting up the PC) as was suggested by Dirk in comment #10. Result: Now emails display instantly when opened. Contacts open instantly now without the couple of seconds delay.

    But now the Reading Pane is greyed out completely.

    So it seems the rogue Dell MediaDirect software was the cause of making the last week with my brand new Dell, a very frustrating experience!

  14. Like just about everybody, I have had enormous trouble with Outlook 2007. I will try the fixes above, but they do not address one major problem – the fact that outward emails with even medium-sized attachments (515 Kb was the latest attempt) sit in the Outbox and send multiple times (up to 24 times for one client) without deleting themselves.

    I have only been able to delete the email or interrupt the Send by killing my online connection.

    Outlook 2003 had this problem – because it was so slow it caused Server Timeouts, and the recommended solution was to increase the Timeout. It seems Outlook 2007 may have the same problem – or are there other causes?

  15. After running fine for months, Outlook 2007 started to perform intolerably. Every five seconds it would stop responding… there would be a significant delay after typing, with seconds passing where nothing appeared on the screen. I would click on something and no response if it happened to occur in that five seconds. I could see the processor off doing something at these intervals.

    I don’t know what caused this but after uninstalling Dell Media Direct and using the fix in number 27 you posters have SAVED THE DAY!!!!!!!!!!!!!

    Thank you so much. I have spent hours trying to track down a solution.

  16. I also have a brand new dell core 2 duo that was experiencing SLOWNESS! I even created a new email acct to make sure the box was small.

    Uninstalled DELL MediaDirect and all is fine now!


  17. I also have a brand new dell core 2 duo 2.2GHz and 4G Ram and outlook 2007 just crunched it. What a joke. I have reverted back to an old Xp machine and 2003 until I can get a reasonable response out of the new dell and 2007. Ran the microsoft patch from 39 above and response times were significantly better. SLOWNESS! what an understatement. I figure running the microsoft patch gives the same performance improvement as removing media direct from what others have posted here. Disk still gets thrashed on startup for some time though. Has anyone done both. If so did you get further improvement in performance.

  18. Forget the microsoft patch above. After a week of extra emails, ready to junk new machine. Quite simply, outlook is unuseable. Removed Dells media direct, and got a reasonable performance increase again.

  19. Thank you. Have a Dell Inspiron 640m, 1.73, 1gb ram.
    Had silmilar slow problems with 2003 so upgraded to 2007. same slowness. Heard it could be a confllict with adobe pro 7 so lost that. same slowness.
    Removed all rss feeds, same slowness.
    ran scanpst.exe, it fixed lots of errors but still same slowness.
    Came here, removed dell media direct.
    All running very well, so pleased.

    As in #10, #33 & #35. It has fixed outlook for me.
    I do only have a very small pst file (40mb) but untill i got here my other searches were for an alternative product to outlook.

    Thank you to all.

  20. For what it is worth – we have noticed that the previous version of iTunes (prior to 7.3.2) had an extra Outlook sync component that is removed when you upgrade to the latest version. Prior to upgrading, removing the add-in from the Trust Center gave us a nice little perfomance boost. Killing the reading pane (turning it off) also made a huge difference.

  21. Assuming that Microsoft folks are still reading this blog. It’s ridiculous that they expect us to reduce our PST file size, access to information is power. I’m the CEO of a medium sized company, just purchased a new Toshiba laptop 2.4Ghz Intel Duo w/4GB RAM (even though only three are recognized). Outlook 2007 was pre-installed, so transfered my large 4.5GB 2003 PST file. WHAT A MISTAKE. Everytime OL 2007 sends/receives, the computer freezes until the action is complete. I’ve installed all the updates recommended by MS including the one above with little or no improvement. I can only say I’m glad that my 50+ employees are still using 2003…

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