I've been working with Office 2016 almost ever since it was released and very happy with it, in general. My PC (Windows 10 64-bit) is always on, and Outlook is always open. The PC itself is very strong, with 16GB of RAM and SSD disks.

Recently I've noticed that after a while (~1-2 hours) that the Outlook was open and running, it becomes very slow. The switch between message is very slow, even when I open a new message and want to attach a file, for example, it takes quite some time to get the files explorer, and even working inside of it (browsing in the folders and so on). When I shut down Outlook and open it again right away, everything is back to normal, until the next time it turns slow like that.

Now, I'm not sure it's related, but it started happening around the time I switched my free AVG anti-virus software to a PAID ESET Internet Security software. Because this is a paid version, I do not want to just throw it away, and anyway it doesn't guarantee that this is the source of the problem. Moreover, I don't have a general issue of the PC running slow. Everything else in my Windows seems to be running just fine.

Yesterday, I also switched between Office 2016 and Office 365 and the situation is just the same. So it looks like it's something related only to Office, and I'm not sure it's because of the ESET software...

Any suggestions on how to tackle and resolve this will be greatly appreciated.

  • Try to remove some cache files from disk cleanup.
    – Biswapriyo
    Sep 2, 2017 at 8:25
  • Any update on this?
    – DankyNanky
    Nov 29, 2017 at 13:03
  • As for clearing the cache and cleanup, I am using CCleaner software. Anyway, that didn't do the trick, and still after a while (usually 2-3 hours), Outlook is getting slower and slower until I exit it and open back again. Then, everything is fine until the next time... I should mention that everything else on my PC (including other Office products!) is working fine all the time and there are no slow-downs like this anywhere else.
    – TheCuBeMan
    Nov 29, 2017 at 16:45

1 Answer 1


This can be categorized as "normal" behavior" in some user-cases. The first diagnosis step would be to run OffCat and see what it reports.

The next thing to do in the office suite is to Disable Hardware Acceleration, the symptoms match:

Additionally, you may experience one or more of the following symptoms that reduce the functionality of an Office program:

  1. An Office program is blurry.
  2. Your screen flickers or flashes.
  3. An Office program is either mostly all white or all black.
  4. Text in your document is not displayed well.
  5. Your Office program crashes.

    6. The performance of an Office program (other than startup and shutdown) is reduced.

Next issue being, if you are using Exchange or Offline Cached Mode. Generally speaking, cached mode's performance is superior, unless the limitations of the OST file are reached.

Now, the next thing to do is ensure your Pagefile has more than 8GB allocated; I say this as Office using Virtual RAM and not standard RAM to operate; this has solved 80% of my users issues with Office 2016.

To check if Outlook or the suite is up there:

Get-Process | sort vm | select name, vm -Last 5

The next step is to ensure you're not using an excessive amount of CPU or RAM (Is ESET scanning in the background?). Check out performance monitor with reports for this one.

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