I use Outlook all the time, so the many problems I have found with the newest version drive me nuts. Especially the speed issue. As a result, I have spent far too much time looking for a solution. I think I finally found one though as Tris explains:
One of the big problems folks have been having with Office 2007 is Outlook. Frankly, it can be a serious dog. Sluggish, serious performance lags. All the things you don’t want in your “latest and greatest” e-mail client.
Looks like, thanks to Mack D. Male, there is a solution…I did this last night and I think it’s working.
I appreciate the nod Tris, but I’m just the messenger. Full thanks should go to Monty and Dell. Who’s Monty? Beats me. But he posted the message on the Microsoft discussion groups with the solution he got from Dell. Instructions are in the post, and in Tris’ post too, but basically the tip is to turn off all the addins in Outlook. You need to be running Outlook as an Administrator when you do this, and you should also restart Outlook after you turn them off.
I have tried this tip on two machines – one where Outlook is a POP3 client, and one where Outlook connects to Exchange. The biggest difference appears on the first one, but both seem faster when selecting messages, changing views, etc. Downloading mail doesn’t appear much faster yet. The only addin I left checked is the Windows Search Indexing.
Microsoft still needs to fix Outlook, but hopefully this tip will help you in the meantime. Let me know if it works for you!
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MasterMaq's Blog 
hmmm… well after 3 minutes of use following unchecking everything except search…. the interface seems a bit quicker but the real problem is still mail receipt when the UI locks up (including so the theme painting is replaced by standard NC PAINT drawing) and email composing freezes.
I tried a tip of turning off "reduce the size of…" under the Mail Format tab… they ‘may’ have helped a tiny bit.
So no more Inbox huh? That sucks.
I’m running with just Inbox and it seems fine to me.
Nick, I’m not sure if it is one specific plugin, or the number of plugins that make a difference. I know Tris is running a few plugins. I am going to re-enable some and see what happens.
Let me know if you run into any issues with Inbox when you re-enable…
Actually, let me know if you want to test an Alpha version that should be going to beta next week. Nothing new, just a bunch of bug fixes.
Nick, I’m using Newsgator desktop sync after moving to Outlook 2007.
What will happen to Inbox?
The check for updates and annoying InstallShield thingy both say there are no updates, but I just checked your blog and noticed that you released NewsGator Desktop… I had no idea…
All my posting about Outlook 2007 has come in handy! On Saturday, Kevin sent me this link, and today…
This actually worked!!! But contrary to the advise, I didn’t have to log-in using admin rights.
It is not important whether this tweak will speed up Outlook by 10% or not, what s the use of it if I can not have 10 or 20 plugins which I may need once in a while? What makes me wonder is, that even one year after releasing a software no improvements are available. Same for Vista btw.
I have a new PC 100 times faster than my old PC, but Outlook is 100 times slower than 8 years ago, so basically it is 10000 times faster to use Office 2000.
They must be sleeping at Microsoft so they didn’t notice yet that the things are not working properly. And I wonder if the same morons are responsible for the friggin Vista slowness, probably yes.