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MatthewBeecheyMobius-0590 avatar image
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MatthewBeecheyMobius-0590 asked GopalAgarwal-4201 answered

Outlook 2016 OST file behavious

I have a client with a 26GB mailbox on 365. The strange thing is his PST file keeps growing to the 50GB limit in a very short period of time. Averaging about 10-14 days.

The only oddity might be the way he does his email filing. When he's actioned an email he soft deletes it. Then when he has time he files emails from his deleted items into folders it they require keeping.

Is there something funny in the handling of emails in an OST file when moving in and out of deleted items that they become duplicated in the OST file. I would have thought any moving of an email between folders just changes the reference to the location and doesn't require duplicating the email stored in the OST or am I wrong?

Any help on this would be great as I'm having to delete his OST file so it re-downloads at least once a fortnight at present. I'm fairly certain on completion of the download the OST file is the correct size but I will double check today just incase he is syncing someone elses calendar who maybe has bad habits of filing meetings with large attachments (I've seen someone with a 5GB email booking before on an Exchange server where the limits were turned off completely)

Any other pointers to what might be going wrong?? To be honest I'm not 100% sure I've checked if his version has all updates but in the environment in question I'd expect it to be up to date.

office-outlook-itpro
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ChristyZhang-MSFT avatar image
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ChristyZhang-MSFT answered ChristyZhang-MSFT commented

Hi @MatthewBeecheyMobius-0590 ,

Welcome to our forum!

In order to further confirm the problem, please provide information about the following problems:

  • What's the version of your Outlook? (File > Office Account > About Outlook). Please make sure you have upgraded your Outlook to the latest version.

  • Do you use manual archiving or automatic archiving?

  • You mentioned that duplicate messages will appear after moving deleted items, right? If so, how did you view it, by searching the mailbox and finding two identical emails?

According to your description, I noticed that you seem to have many concerns about the large mailbox size. As far as I know, exporting mail to backup is also a good way to reduce the mail size. For more information, please refer to: Export or backup email, contacts, and calendar to an Outlook .pst file.


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Hi Christy - The emails are getting duplicated visibly - The problem is the OST file is growing a lot faster than any other normal user I deal with. It just grows and grows doubling in size in 10 days on average so I'm wondering if internally the way OST file stores the email is behaving strangely because files are moves in and out of the deleted items folder?

Most users with a 25GB mailbox won't hit the 50GB limit on their OST for 6 months or more but this guy is hitting the limit in 2 weeks or less. Each time rather than compressing which takes too long I delete the OST, it redownloaded the ~25GB of data and then hits 50GB again a short time later.

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ChristyZhang-MSFT avatar image ChristyZhang-MSFT MatthewBeecheyMobius-0590 ·

Hi @MatthewBeecheyMobius-0590 ,

Thanks for your reply!

According to my test, the OST file will not grow when moving messages to deleted and archiving deleted messages. As far as I know, the OST file of the exchange account mainly stores: your mailbox data (mail, calendar, contacts, tasks, notes and journal folders), hidden items and other “overhead” as found in a pst-file, public Folder Favorites and shared folders of additional mailboxes linked to your Exchange account. And according to my research, there is no official document mentioning that the changes of OST files will be related to deleted files or archives.

Considering the impact of some add ins, It is suggested that you try to start outlook in safe mode(win+R>type: outlook /safe) to check whether it works normally. If it doesn't work, considering the impact of some third-party programs on your computer, please try to perform a clean boot for windows and check if the issue still occur.

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He isn't archiving the emails. He's moving them from his inbox or sent items by deleting them so they sit in deleted items. Then he is moving them back into subfolders or his mailbox for filing.

I will check for addins but I'm pretty sure he doesn't have any installed but its been going on a while so I've lost track of what I have and haven't checked.

Matt

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ChristyZhang-MSFT avatar image ChristyZhang-MSFT MatthewBeecheyMobius-0590 ·

Hi @MatthewBeecheyMobius-0590 ,

I am writing to see how everything is going on with this thread. Should you need more help on this, you can feel free to post back.

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GopalAgarwal-4201 avatar image
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GopalAgarwal-4201 answered

Hi @MatthewBeecheyMobius-0590 ,

I think you have a large amount of Public Folder Favorites, or you are accessing shared mailboxes. If you have configured Cached Exchange Mode, then shared items also keep downloads in the OST file that can increase the size of OST so quickly.
I suggest you turn off the Cache Mode for shared mailboxes and access it through Outlook Web.

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