OST file size while limited cache

Bas de Jong 1 Reputation point
2021-03-15T09:32:18.273+00:00

Hello all,
unfortunatly there are a ton of messages to find on the internet that do not resolve my issue.

GPO's
GPO: download full items
GPO: Cache three months

Example mailbox:
Exchange365 size: 9080Mb
created days ago: 972
calculation: 9080Mb/972days*90days=840Mb

current User OST size: 5Gb (excluding the ost's for shared mailboxes which have diffrent ost files)

Tried:

  1. new outlook profile, grows to 5Gb in 2 days
  2. find folder size, size is not there
  3. clean function
  4. new windows profile

what else can i try to reduce the OST file size as this should only be 840Mb instead of 5Gb.

Kind regards

Outlook Management
Outlook Management
Outlook: A family of Microsoft email and calendar products.Management: The act or process of organizing, handling, directing or controlling something.
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  1. JeffYang-MSFT 6,241 Reputation points Microsoft Vendor
    2021-03-16T03:08:25.01+00:00

    Hi anonymous user

    Welcome to our forum.

    Sounds like you might have some misunderstandings about the relationship between .ost data file size and the size of your mailbox.

    As I know, it is normal that your OST file size is not equal to the size of your cached mailbox items. For Exchange email account, your OST file caches not only mailbox items such as mail, calendar, contacts, tasks, notes and journal folders but also caches things like below:

    1. Hidden items and other “overhead” as found in a pst-file.
    2. Public Folder Favorites.
    3. Shared folders of additional mailboxes linked to your Exchange account.
    4. Some outlook desktop client settings will also be cached to your OST file.

    If you would like to reduce the size of your OST file, the first thing I think is that you could try is to modify your Exchange cache settings to cache less email messages to your local datafile, then find the location of your OST file, exit your Outlook client, rename your OST file and restart your Outlook client, your mailbox will be recached in a new smaller OST file.

    Also, there are some other methods you could use to reduce the size of your OST file, please check this article:
    What is stored in the ost-file and why is it larger or smaller than my mailbox?
    (Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)

    Hope this can be helpful.

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