Outlook slow-down suggestions


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A reader is having a problem with some sluggish machines running Outlook – we suggest some possible cures.

Al C. writes with a question about Outlook, he gave some details and had covered some obvious bases (virus infection, checked the Microsoft Knowledge Base), in summary:


“I have 4 machines that are experiencing a major slowdown in Outlook.  When you first open it – it takes a long time to load and then when you select an email for viewing it takes an unusually long time (over 1 min) to display the message.”

It’s always hard to fix these non-specific problems, let alone do it from afar.  All we can do is suggest some additional lines of investigation or repair.

It’s possible that the problem isn’t Outlook at all, but something else on the computer. Outlook is so resource hungry that other problems on your computer may manifest first as a slow-down in Outlook.

However, from your description that doesn’t seem to be the case. The fact that the problem is on starting Outlook would suggest that it’s a PST data file issue. Outlook will perform a data file check and fix whenever it starts – if there’s a problem there should be a message saying that a data file problem is detected and will be fixed. This happens in the background for Outlook 2007.

However sometimes the PST file problem isn’t detected by Outlook – yet difficulties in accessing data will make Outlook sluggish.

That it’s happening on multiple computers is strange. It’s tempting to blame the latest Microsoft patches, but I think it’s unlikely.

The ‘Detect and Repair’ option you mention won’t help with Outlook data file problems like this. ‘Detect and Repair’ is part of the Office installation system – it will check that all the programs and settings are correctly installed, but it doesn’t check data files like Word documents or Outlook PST/OST files.

Even though Outlook has an in-built PST/OST repair system there’s a better option. SCANPST is installed with Office and will be in a sub-folder under /Program Files, wherever Outlook.exe is located you’ll also find SCANPST.EXE


Don’t confuse SCANPST.EXE with SCANOST.EXE which is for users on Exchange Server systems. Even then Scanpst.exe applies to OST files.

Find out where your PST file is located and note it down. Close down Outlook entirely and then run SCANPST (double-click on it in Explorer), browse to the PST file and let the scan begin. It can take a long time if, like most people, you’ve gathered your life into Outlook.

Another possibility, though unlikely based on what you’ve said, is that the PST file is heavily fragmented on your hard drive. The PST file can get very large and split into various locations around the hard drive platters. Run the Windows Defrag tool to optimise your hard drive, including the PST. You must do this with Outlook shut-down. The benefit is usually marginal but it’s worth a try.

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