Archiving Problems

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My Outlook 2016 ost mailbox was about 15 GB so today I tried to archive everything from 2010 - 2016 to a pst file, using the built in tool (File > Tools ?\> Clean Up Old Items). I havetwo questions:

1. When I look at "folder size" within Outlook, it now shows about 1Gb, which is about what I'd expect. But if I look at the ost file (app data > local > microsoft> outlook), the ost file is still 115 GB. Why? I closed and restarted, still the same size.

2. In several folders it left old messages going back years and didn't archive them. Is there any way for me to have it do another run and catch the old messages and archive them to the SAME pst folder with the folder structure intact? I can try to do it manually but that will waste a lot of time.

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1. You need to compact it. Outlook will work on it as the computer is idle, but you can start compacting and head to lunch. It will probably take a few hours, but you can stop and start it as needed. See How to compact an Outlook data file (*.pst) if you don't know how to compact.
Sorry about missing #2... I have a problem with clicking Post before i'm finished. :(
On 2, it depends on why they were missed - are they marked to not be archived or did you do something to change the last modified date?

See AutoArchiving by Received Date in Outlook for a registry key to archive by received date.
Thanks for your response. Neither on #2, but I just ended up transferring them manually. Unfortunately going from a 15 gb file to a 500 MB files doesn't seem to have made a bit of difference with regard to Outlook hanging and being slow. Which is pretty much something I just live with as a fact of life when it comes to Outlook, but since I'm always told it's due to file size I figured I'd give it a try. It's the only program that is always slow, whether I'm on my desktop or laptop, both of which are high powered machines :-(.
At 15 GB, it could be the data file size, but the number of messages in the inbox (because its the folder you use the most) can also cause it to be less responsive, but only if you more than like 5000 or so. This is due to outlook displaying the messages in the view.

What type of email account do you use? Do you have any/many addins installed?

Outlook will be slower on computers with less ram - but if you have more than 8 GB, it shouldn't be a factor most of the time - even 4 GB should be ok unless you are doing a lot of intensive work in other programs.
Thanks Diane. I think I spoke too soon. It has definitely sped up very significantly, though at times it does still hang when switching between different views/folders.

I use multiple Exchange mailboxes on O365. I suspect having multiple mailboxes might be part of the issue. But now that it's improved significantly I'm going to watch closely and try to diagnoses the cause of any remaining problems. It's not the machines that's for sure, the laptop has 16 GB of RAM and the desktop has either 32 or 64, can't remember which.

One other thing I suspect is OL has some issues running at native 4K (no scaling of any type). I've had many instances where it starts to freak out, and if I minimize it to a smaller size suddenly responds instantly. I believe this is an OL issue because I don't encounter it with any other programs. I can run much more memory intensive programs like AutoCAD at native 4K with never a hiccup.

Anyhow, thanks for your help as always :). I'm happy at the improvement I'm seeing here.
One other thing I suspect is OL has some issues running at native 4K (no scaling of any type).
Possibly. I know there are issues if the scaling is set too high (over 125 or 150%)

I suspect having multiple mailboxes might be part of the issue.
I have 4 Office 365 Exchange + 2 shared mailboxes autpmapped & 2 sharepoint mailboxes. I don't have problems, at least not on my desktop (32 gb). It's slower on my 8 GB 2-in-1 but it could just be my frustration - i get annoyed with the 11" screen and small keyboard.
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