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Depending on the size of your PST and other factors, a compacting operation can take a long time. I recommend when to do the operation.

Leo, I'm using Windows 7 and Outlook. I'm compacting my PST file after clearing out thousands of emails. Compacting has been running for about five hours. I'm not getting an error message, but occasionally it says, "Outlook not responding." But then the message goes away. Should I just let it run? I don't think it's hung; it just says compacting. It's still receiving inbound emails, so I don't think it's frozen. Please advise.

In this excerpt from Answercast #13, I look at why Outlook might be giving a "Not Responding" message when you compact a PST file.

Outlook not responding

Absolutely. Let it run. I've actually done this in the past.

Depending on the size of your PST, the number of email messages, the speed of your computer, the speed of your hard disk, and whatever else might be going on at the same time while this is happening, a compacting operation can take a really, really long time.

Compacting Outlook

I know that when I used Outlook regularly and I went through a process like this, I actually set it to 'compacting' and let it run overnight so that in the morning, it was usually done. It's definitely a multi-hour process if it's got a lot to clean up.

Why you get "Not Responding"

The Not Responding is not surprising. At times, the program is focusing solely on the compacting operation and doesn't have time to get back to Windows when Windows asks it, "How ya doing?"

That is obviously a mischaracterization... but it's kinda sorta what really happens. When a program is running, every once in awhile, Windows sorta says, "Hey, how you doing? Are you still running? Can I use the processor for a little while?" That kind of thing.

When the program is too busy to respond to Windows, you get this "not responding" error message.

It can be temporary. Obviously, as the program does its work (and moves on to the next stage of the compaction, perhaps), it then has a few seconds to respond to Windows and let Windows know that, "Yes, everything's fine."

So, in a case like this, especially while it's still receiving email, I would not worry about this. I would let it run to completion.

Schedule the operation

Next time, I would absolutely do it at a time of day where you can feel comfortable letting it run for a really, really long time:

  • If you're at work, let it start before you leave for the day.
  • If you're at home, let it run overnight.

Like I said, it just can take awhile; it's not unexpected.

Article C5272 - April 30, 2012 « »

Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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1 Comment
May 2, 2012 6:45 PM

Taking outlook off line helps speed up compacting process. As there are no incoming mails that goes in the folder that is being compacted, the process goes a bit faster.

Outlook does not let you do anything during compacting anyway so there is nothing to lose by taking it off line.

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