If you are stuck using Microsoft Outlook to send those TPS reports at work, you've already experienced just how painfully slow it can get—but with a few quick tips you can make it usable again.
Install Service Pack 2 (or later)
While you might keep up to date on all of your Windows patches, too many people are running outdated versions of Microsoft Office (not to mention other applications). You'll want to install the very latest service pack—because Service Pack 2 has fixed a ton of performance issues for users with large mailboxes or anybody using IMAP to access their email.
Download Complete IMAP Items (Like POP Does)
When you are using IMAP to access your Gmail (or other email) account, you'll probably notice that Outlook can hang, stutter, and just generally become completely unusable—but it works just fine with POP accounts. You can make the whole experience a lot better by telling Outlook to download the entire message every time you synchronise so you won't have to wait while it slowly grabs the message off the server. Head over to the Send/Receive Groups panel by using the Ctrl+Alt+S hotkey, then drill down into your account and choose "Download complete items including attachments". The first time Outlook syncs with your mail server, it might take a little longer, but you should notice a significant improvement overall.
Force Outlook 2007 to Download Complete IMAP Items [How-To Geek]
Setup Auto-Archive to Clean Your Mailbox
Keeping a nice, clean mailbox is probably one of the most obvious, but also most overlooked aspects of speeding up your Outlook experience. You can do it yourself by setting up a separate personal folders (PST) file, and then moving old email over there on a regular basis. If you don't feel like managing the archiving process yourself, you can turn on the built-in Auto Archive feature by heading into Tools -> Options -> Other and setting up your preferences for when to archive—you may need to tweak them to fit your own emailing behaviour, but the key is to keep your daily mailbox nice and small.
Configure AutoArchive In Outlook 2007 [How-To Geek]
Compact Your Personal Folders (PST) File
This is one of those tips that almost all long-time Outlook users know, but it's still important to mention. All of your email is stored in a single .PST file that grows larger and larger as time goes on, but deleting messages isn't good enough because the file never gets any smaller. You'll need to head into the Files -> Data File Management menu, then using the Settings button to take you to the dialog where you can actually compact your mailbox, shrinking the file down and potentially saving you a ton of disk space.
Quick Tip: Easily Compact Outlook Data Files [How-To Geek]
Run the Inbox Repair Tool
You've probably never thought of running the built-in Inbox Repair tool unless you absolutely have to, but if your Outlook frequently crashes and requires restarting from Task Manager, you should probably give it a run to fix all the errors you didn't even realise were there. Since your personal folders file is effectively a database, it's important to keep it clean and free of errors. You'll need to head into your Outlook installation folder, and then find the scanpst.exe file to start the repair process.
Fix Your Broken Outlook Personal Folders (PST) File [How-To Geek]
Disable Outlook's RSS Feature
If you aren't using Outlook to read your RSS feeds, you might not realise that it's still synchronised to the Internet Explorer common feed list. There's really no reason to keep this feature enabled, and you can easily disable it by heading into Tools -> Options -> Other -> Advanced and removing the checkbox from "Sync RSS Feeds to the Common Feeds List". Don't forget to delete any RSS feeds once you are done.
Make Outlook Stop Using Internet Explorer's RSS Feeds [How-To Geek]
Save Attachments (So You Can Delete the Messages)
Chances are good that the majority of used space in your mailbox is taken up by all those attachments that everybody keeps sending you. After a while, your inbox is going to get so gigantic that Outlook can't help but slow down a little, but you can easily find all of the attachments and save them somewhere else before you go through a big mail cleanup—just use the free OutlookAttachView utility to save them to a folder easily and quickly.
Use the Mailbox Cleanup Wizard
It's not that difficult to sort a few columns in your inbox and figure out which messages are wasting the most space—but if you've got a complicated set of folders that you use to organize your email, you can quickly view all email that is older than a certain date, or too large to keep around. Head into the Tools -> Mailbox Cleanup wizard that gives you loads of options to quickly find and delete messages you really don't need to keep around anymore.
Quickly Clean Your Inbox in Outlook 2003/2007 [How-To Geek]
Disabling Plugins Can Seriously Speed Things Up
There are loads of great add-ins for Microsoft Outlook that add all sorts of great features, but often there are add-ins installed that are unused, unnecessary, or just pointless—and those are most likely the biggest cause of Outlook slowing down to a crawl no matter what you seem to do. You'll need to head into Tools -> Trust centre and click the Go button to edit your COM Add-ins, though Windows 7 or Vista users might have to open Outlook in administrator mode to be able to disable some of them. In my experience dealing with Outlook problems, this is the hidden one that most people never think of, but gives the biggest benefit overall.
Make Outlook Faster by Disabling Unnecessary Add-Ins [How-To Geek]