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. re: Patrick Philippot

    If it’s thread synchronisation, have you tested while setting the processor affinity for outlook to only use one execution core? And confirmed it then is ok?


  2. Guys I’m not that technical but I think I’ve uncovered at least a small part of the mystery of Outlook 2007 running slowly… (i’m not on a Dell)

    I feel that I should share this because it’s just solved my problem – I think…

    I’ve spent the last few days vey frustrated with the 100% CPU freeze every few minutes because of Outlook. I tried it taking it offline – no change (well a slight improvement but its still unusable). I racked my brain to think what I’d changed recently to make it suddenly max out all the time – nothing came to light. I scoured the net all day today and I shrunk my pst file to below a gig – no change, I tried everything I could find on the net – nothing improved it.

    Then (off line) I noticed a little magnifying glass icon bottom right near my MSM icon. I hovered over it and it’s said “synchronizing” or something like that I right clicked and selected “stop synchronising”. Know what? Ever since then Outlook has been behaving perfectly!!! Really! No maxing out, no stalls nothing its fine again!

    I hope this helps someone because I know how frustrating it is… And I’d love to know why its fixed for future…

  3. Ok, I’m not sure if this will apply to everyone but this is how i fixed my typing delay on Outlook 2007, Windows XP.

    Uninstalled all Addins, uninstalled Microsoft Intellitype (ergonomic keyboard 4000), uninstalled microsoft intellipoint, uninstalled display fusion, run Oulook in Safe mode (cmd > outlook /safe)

    As I’m typing this message i’m seeing no delay whatsoever… my delay problems affected XP system wide, but they were especially pronounced in Outlook 2007.

    Should be a fun week for me (desktop support), job security I guess.

    Good luck all.

  4. I’ve read through this entire thread. I have a DELL Desktop using WinXP with Office 2007. It was running fine for over a year, until about 2 weeks ago.

    Now, when I’m creating an email message, if I don’t get it out fast enough, my outlook freezes. No cursor, and even the mouse cursor in front of outlook windows disappears. No redraw happens (not even “Not Responding” in the title bar); if I drag a window in front of it, that image never disappears.

    But the other apps are still usable. So I can look at task manager, which shows exactly 50% utilization (but not on just one CPU, it’s split over 2 CPUs, but exactly 50%, which seems to indicate a single CPU at 100%). One night I let it run all night to see if it would catch up… it didn’t.

    So now I’m killing outlook every once in a while.

    Although I’m on a dell, I don’t have mediadirect, so I can’t uninstall it. (Drat!)

    And I’m not on Vista, so the TCP doesn’t help me.

    I’ve got a few add-ins, but they are all the same as they were. However, one of the recent automatic updates was upgrading XP SP2 to XP SP3, so I wonder if it’s related to that. Since that time, my email is taking a lot longer to download, and I think it was about that time that these crashes started.

    I tried removing contacts (one of the posts near the top); didn’t help. I also tried uninstalling and rinstalling, doing a repair, and doing an office diagnostics. The diagnostics did send in an error, but didn’t tell me what it was. It said it fixed it, but I’ve noticed nothing different on my side.

    My last thing to try from the above posts is to split my 3 different POP checks into different profiles. But this seems to be a download helper, not a drafting-email-freeze helper.

  5. Splitting my POP boxes into different Send/Receive profiles helped the download speed, but didn’t help with my freeze when drafting email messages.

    I’m going to start the “disable add-in” walk, but I don’t have much hope for it because these have been the same for months (unless an automatic update changed something).

  6. BTW, I don’t have MediaDirect, but I do have something from DELL called “Media Experience”. It doesn’t seem to have an outlook add-in. Anywone know whether this is related to “MediaDirect”?

  7. Hi all,

    this may be of use to someone.

    My problem was that Outlook 2007 took minutes (1-5 mins usually) to download mail from my POP3 accounts. It would invariably download from my one Hotmail account pretty much instantly.

    I tried all the various fixes listed here without success. Finally I went in to the individual accounts and started tinkering. I found that if I put an invalid entry in the incoming mail server box on the default account then, if I hit send receive the recieve operation on that account would immediately fail but the other accounts would then immediately spring to life and download all their messages. I should state that all the accounts are held on the same domain hosted by 1&1.

    Anyway, although I was sure the settings were all correct (I did after all get all my mail on all accounts – it just took a long time), I decide to delete that account and then make a new account with all the same details entered – voila! full speed Outlook 2007.

    I should also note that I tried making another account the default before deleting the original default account and that changed nothing.

    Sorry for the ramble, maybe, just maybe it could help someone.

    Best wishes,


  8. We have XP Pro SP3 with Office 2007, we’ve used 2007 for a while now and only recently outlook started miss-behaving, i noticed that whenever i preview or open an email with attachment (no matter what size) outlook does not reapond for 30 sec. to a minute but finally opens, its fine with emails with no attachements, we use .ost files with exchange 2003, the .ost file is about 1/2 GB so the 2GB or 4GB size file does not apply to us.

    The only significant changes we’ve made recently is apply SP1 (which by the way can not be uninstalled) so we can’t verify if it is SP1, we also installed SP3 for XP, this however improved overall performance of the PC but not Outlook, so, since Microsoft is sitting still and have absolutly no fix,and only trying to make us all move to Vista and Office 2007, our entire corporation has decided to dump office 2007 and go back to Office 2003.

  9. I installed Office 2007 recently and run it with XP, I have a wickedly fast system with 3.0 Xeon processors & 4 gigs of memory, where everything is fine except Outlook. The problem I’ve had is that there is a delayed action to key strokes and text appears spasmodically in batches sometimes several seconds after hitting the keyboard. I need Outlook to run well & we also need the BCM to help develop new business. I have to say Outlook runs like a dog a really bad dog of an application. When the parent company of Microsoft is giving 5 gig spaces away on Hotmail, how on earth can anyone figure that we can now use 2-400mb mailboxes? I have the latest Outlook.exe file along with MSPST32.DLL where both versions are 12.0.6315.5000.. Where are the obvious steps I am missing here? I even emailed to let them know how I felt. This is next to useless.

  10. I installed Office 2007 recently and run it with XP, I have a wickedly fast system with 3.0 Xeon processors & 4 gigs of memory, where everything is fine except Outlook. The problem I’ve had is that there is a delayed action to key strokes and text appears spasmodically in batches sometimes several seconds after hitting the keyboard.

    I need Outlook to run well & we also need the BCM to help develop new business. I have to say Outlook runs like a dog a really bad dog of an application. When the parent company of Microsoft is giving 5 gig spaces away on Hotmail, how on earth can anyone figure that we can now use 2-400mb mailboxes? I have the latest Outlook.exe file along with MSPST32.DLL where both versions are 12.0.6315.5000.. Where are the obvious steps I am missing here? I even emailed to let them know how I felt. This is next to useless.

  11. My setup is similar to John’s (#135): wicked fast Intel quad-core, 4 GB of RAM, and 10,000 RPM Raptor drives. You probably can’t build a faster machine. I’m running Outlook 2007 on Vista Ultimate. No indexing, no addins. And yet, every time an email comes in, if I’m typing an email, it just freezes. Mind you, this is a quad-core. There’s no excuse for Outlook single-threading these operations. I’ve read a lot about this problem and the only thing I’ve got left to do is reduce my PST size and turn off filtering. I can’t do the former — I run a software business and I need to maintain ready access to lots of emails on projects. I don’t want to turn off my one filter or I would be swamped with spam. BTW, we run our own mail server (MDaemon), which is directly connected without firewall or router, so this isn’t a TCP/IP issue, methinks.

    I’m generally happy with most of Office 2007 (after taking months to figure out where everything is again). But, Outlook is simply a bad piece of software and they should get to fixing it.

  12. I have an office of over 50 PC’s creaking to a halt becuase of outlook.
    Every morning hours and hours are wasted while people wait for their PC’s to come back alive.
    Some have even resorted to going and using Exchanges webmail client to use their emails.

    We are probably going to have move to a different client so will be ditching exchange as well.

    I never thought I would ever even contemplate lotus notes (just thinking about it makes me cringe) but something has to be done becuase it is probably costing the equivelant of one persons salary in wasted time.

  13. I searched for Outlook 2007 slow on XP and found this blog. My issue with Outlook is not just that it runs slow, but it seems to cause my entire computer to run slowly. I only upgraded the Outlook office program from 2003 to 07 and left all the other 2003, but now Word is slow, PP is slow…it’s really frustrating.

  14. further to my 64) posting in July 2007. I’ve now got a Dell Inspiron 1525 with vista home premium and have created a new pst file by copying and pasting tasks and contacts from my old pst file. Soon after creating the new pst file the ‘reading pane’ no longer worked (again!), moreover the cursor was blinking very fast much of the time indicating processor activity whilst Outlook was open. So I uninstalled the (rather useless) Dell MediaDirect programme. Lo and behold my reading pane in outlook 2007 is now working fine and the blinking cursor has stopped. Maybe, I’m guessing, some component of my outlook data created the ‘reading pane’ problem?

  15. I bought my self a $2000 custom PC with I7-processor, 6 Gig 3-channel RAM, Raid 0 with 10.000 rpm raptors, all the best stuff. Running Vista 64 ultima and installed Outlook 2007. I thougt from now an can work like flying. Great disapointment. Outlook can not even follow the speed I am typing. It’s often 3 words behind. I am on exchange server and my local folder file is 2.6 Gig – sync with my exchange server. I need that size because I am working with many clients in the travel bussines. If I try to send an email it freeze often for over 30 seconds before the email final sends out. During that time you can’t advance with anything in outlook. Sometime it freeze over a minute. I allready unchecked all add on’s except indexing. Haveing the newest hardware but working like it’s in the mid 90’s is a real disapoint. My work productivity is slowed down to the point there I have to use my lunch break to get the work done. It’s crazy. Why does it take microsoft so long to solve this known problem?

  16. I’ve been experiencing dreadful performance from Outlook 2003 on Vista, but using the command as mentioned by Bazza:

    netsh interface tcp set global autotuninglevel=disabled

    makes an incredible difference. My laptop only has 1GB RAM, so I’m runnign without all the pretty graphics (no big deal) but suddenly Outlook responsiveness is amazing.

  17. Bazza no 27 rules. I like everyone else was desperate for a solution. Bought a new notebook Compaq TX-1025 dual core AMD something and 4GB RAM, Vista 64. After loading Outlook 2007 – brought my system to a screeching halt. Looked at each process and researched it and still saw the disk activity way too high and could not figure it out. Willing to try anything and was going to a frsh install this weekend. I performed the “netsh” fix listed by Bazza and my troubles disappeared, eventhough I use a cable modem and Netgear router. Isn’t Netgear owned by Cisco?? Anyway, THANK YOU Bazza.

  18. MattR, what’s your experience with the new SP2? I have tried the February CU (same as SP2) for Outlook 2007, and I did not notice apparent performance improvements.

    For anyone who seriously want to measure the improvement for SP2, please make sure you record some performance data before the upgrade so that you have some data to compare with after the upgrade.

  19. Installe Office 2007 SP2 today and OUltook is ways slow, no improvements when launching it or worse, checking for new messages.

    Problem though is that I have 3rd party apps (not add-ins), for example, to sync Outlook on a USB key and now they don’t work anymore, all crashing when using mspst.dll

  20. I had the same problem, where it takes lot of time to open any emails, or any folders.

    I have disabled all addins, rss feeds. This didnt changed anything.

    Atlast I got some relief when I checked ” use Cached Exchanged Mode”, which was actually unchecked for me.

    May be some of you can have a try on that.

  21. Outlook 2007 Slow Response Issue

    Just wanted to pay homage to ‘Dirk’ the originator 2 years ago(posting below) for the ‘uninstall Dell’s MediaDirect programme’. Worked a treat… dont you just love IT!!! LOL

    Not had other similar issues to the rest of you guys, will post if i do.

    Regards All

    February 24th, 2007 at 3:24 am
    After many hours of investigation (and using the Vista Reliability & Performance Monitor) I have found the culprit for my Outlook 2003 performance problems on the Dell Notebook. The dell MediaDirect component was causing all the grief. Uninstalled and all is OK!<

  22. This Outlook issue is killing my day, my productivity. Microsoft people need to get out of their shoe boxes and see the world. I don’t think they even know how bad is OUTLOOK is screwing up people’s life.
    The dialog says looking for solution, what a B.S.. Sounds like someone just pull something out of their rear.
    The dialog says checking datafile because it wasn’t closed properly. Sounds like someone just got nothing better to do but need to justify their paychecks.

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