Outlook fix - classic
Outlook running slow or hogging memory
If classic Outlook is slow to open, laggy or eating memory, the usual culprits are heavy startup add-ins and a bloated OST/PST data file. Disable non-essential COM add-ins, keep the mailbox trimmed, empty bulky folders and repair Office - or we'll speed it up for you remotely in minutes. Rated 4.9 on Google.
- ● Classic Outlook on Windows
- ● Fix in minutes remotely
- ● Microsoft Partner
The quick answer
Two things slow Outlook down most
A slow, laggy Outlook nearly always comes down to two things: a heavy add-in loading at startup, or a giant data file (OST/PST) that Outlook has to wade through. Tackle these first on classic Outlook for Windows:
- Disable startup COM add-ins. Add-ins from PDF tools, CRMs, antivirus and old toolbars can each add seconds to launch. Go to File > Options > Add-ins, at the bottom set Manage: COM Add-ins and click Go, then untick anything you don't actively use. Restart Outlook and see how it feels.
- Shrink the mailbox Outlook keeps offline. On an Exchange or Microsoft 365 account, go to File > Account Settings > Account Settings > Change and drag the Mail to keep offline slider down to 3, 6 or 12 months instead of All. This keeps the local OST small and fast. Older mail still lives on the server and stays searchable online.
A quick test to confirm add-ins are the problem: press Windows key + R, type outlook.exe /safe and press Enter. If Outlook is nippy in Safe Mode (add-ins off), you've found your culprit.
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Deeper fixes
Trim, tune and repair
If it's still sluggish, work through these - they clear the most common causes of high memory and a laggy interface:
- Empty the bulky folders. Right-click Deleted Items > Empty Folder and clear out Junk. Thousands of old items in these folders bloat the data file and slow everything down.
- Keep the OST/PST size sensible. A data file that's grown to tens of gigabytes is the classic cause of a slow, laggy Outlook - startup, sync and search all suffer. Trimming the offline slider (above) and clearing junk keeps it lean.
- Check graphics rendering if it's stuttery. On older builds of classic Outlook there was a File > Options > Advanced > Display tickbox called Disable hardware graphics acceleration. Microsoft has since removed that option from current Microsoft 365 builds - Office now switches problem graphics cards to software rendering automatically, so there's usually nothing to toggle. If scrolling still stutters, update your graphics driver, or in Windows go to Settings > System > Display > Graphics, add Outlook and set its GPU preference.
- Repair Office and stay updated. Right-click Start > Installed apps > Microsoft Office / 365 > Modify > Quick Repair. Then run File > Office Account > Update Options > Update Now and keep Windows Update current - performance fixes ship regularly.
Good to know: none of this deletes your emails. Trimming the offline slider only changes how much is cached on this PC; on Exchange, 365 or IMAP everything stays safe on the server and re-syncs. If you're on a POP account (mail stored only locally), tell us first and we'll back it up before any changes.
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// GOOD QUESTIONS
Frequently asked
Why is my Outlook so slow to open?
The two big causes are heavy add-ins loading at startup and a bloated OST/PST data file. Disable non-essential COM add-ins under File > Options > Add-ins, and shrink the offline mail slider to 3-12 months. Test with Safe Mode (outlook.exe /safe) - if it's fast with add-ins off, an add-in is the problem.
How do I stop Outlook using so much memory?
Trim the local data file: empty Deleted Items and Junk, reduce cached mail to 3-12 months so the OST stays small, and disable add-ins you don't use. A giant OST/PST is the usual reason Outlook hogs memory and feels sluggish. An Office repair often helps too.
What is the offline mail slider and is it safe to reduce it?
On Exchange and Microsoft 365 accounts, Outlook keeps a local copy of recent mail (the OST) so you can work offline. The slider under Account Settings > Change sets how far back that copy goes - 1, 3, 6, 12 or 24 months, or All. Reducing it to a few months keeps Outlook fast and doesn't delete anything - older mail stays on the server and is still searchable online.
Where's the 'disable hardware graphics acceleration' option gone?
Microsoft has removed that tickbox from current Microsoft 365 builds of classic Outlook. Office now detects problem graphics card and driver combinations and switches to software rendering on its own, so there's usually nothing to toggle. If Outlook still stutters, update your graphics driver or set Outlook's GPU preference under Windows Settings > System > Display > Graphics.
Does a big PST or OST file really slow Outlook down?
Yes - it's the number-one cause of a slow, laggy Outlook. Files that grow to tens of gigabytes make startup, syncing and search all crawl. Keeping the file trim (reduce cached months, clear Deleted Items and Junk) is the single most effective fix for most people.
Can you speed up Outlook without me doing all this?
Absolutely. Via Splashtop SOS we phone first, you click one link, and you watch us find the add-in or bloated data file that's dragging Outlook down and fix it - usually in a few minutes. We never need your email password and access ends the moment we're done.
Tired of watching Outlook crawl?
We'll connect securely, spot the add-in or bloated data file that's dragging it down and get Outlook snappy again - usually in a few minutes, while you watch.
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