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Slow Outlook downloads could indicate problems in writing to the disk. I walk through a series of steps to clean things up.

When downloading email using Outlook, it seems to require all CPU power and it takes forever. The same emails can be downloaded in seconds with my smartphone or iPad using the same connection. Why does Outlook make such hard work of it?

In this excerpt from Answercast #71, I look at an Outlook installation that seems to be having a hard time writing information to disk.

Outlook is slow

My initial reaction is to immediately focus on Outlook's need to store the file on your hard disk.

My guess is (and this is just a guess, but it's an educated one) that the PST file itself is either full or fragmented or not compacted.

PST file is "slow"

In other words, Outlook is spending all of its time not in downloading your mail (that part's easy as you've seen with your other devices). Outlook is spending all of its time (and all of its resources), trying to put that email into its storage file, into the PST file.

So, I would do about two or three different things.

Check the disk

One, I would run ChkDsk /R on that hard drive in case it's a hard drive problem that's causing Outlook to have trouble.

A bad sector that happens to be in the middle of your PST could cause exactly what you're seeing.

Defragment the drive

I would defragment your hard disk, if you haven't.

A fragmented PST file that is severely fragmented could easily cause the kind of behavior that you're seeing here as Outlook has to run around to all different places in the PST file to update the location of your email, to add it here, to update an index there, to update the list of your emails elsewhere... So anyway, defrag the drive is what I'm saying.

Compact the PST file

And then finally, it's worth considering compacting the PST file. If you've done a lot of deleting of email and moving emails around and so forth, the PST file itself can internally get kind-of sort-of "fragmented," much like a hard drive. If you defrag it, which in Outlook terms is "compacting it," then you can also improve its performance.

The way to do that is to right-click on the Personal folders (or "Outlook PST," or whatever it's listed as in the left-hand pane of your Outlook window); click on Properties and in (I believe) Advanced (it may just be right there), there's a button that says "Compact Now."

I'll give you a warning: compacting can take some time. It can actually take a fair amount of time if your PST is large. So this is the kind of a thing that you might want to set up to run overnight. Set it up before you leave work, set up before you go to bed... whatever, but let it chug on it overnight.

Final cleaning

Then to bring things slightly full circle... Because modifying the PST (compacting the PST) actually causes a lot of disk activity, it might also be worthwhile to then (after the compaction is done) exit Outlook completely and defrag your hard drive again.

It's very possible that all of the manipulations that Outlook has to do to compact a PST could result in a fragmented PST on the hard disk.

So those are the three things:

  1. ChkDsk /R;

  2. Defrag your hard disk;

  3. And compact your PST.

See if that doesn't improve things quite dramatically.

End of Answercast #71 Back to - Audio Segment

Article C6049 - November 19, 2012 « »

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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
November 23, 2012 6:39 PM

Leo was correct when he stated "I'll give you a warning: compacting can take some time. " I had a pst file which was inflated to 20 GB. I let it compact, resulting in a file of 5.8 GB. This compacting took 25 hours and 40 minutes. The computer did not have to do other tasks during that period and was thus fully devoted to this task.

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