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RuslanIgnatjev-9205 asked JadeLiang-MSFT commented

Does Outlook keep all attachments in .ost file?

Hello,

Does Outlook keep all attachments in .ost file? Or where are they stored when message arrives to users mailbox?
If they are stored in .ost file, then can we control whether attachments will go into .ost file or not? Will it reduce size of the .ost file?

Thanks in advance!

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Hi @RuslanIgnatjev-9205

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JadeLiang-MSFT answered JadeLiang-MSFT edited

Hi @RuslanIgnatjev-9205

Welcome to our forum.

Does Outlook keep all attachments in .ost file?

If you are working with IMAP account or Exchange account in cached exchange mode, the .ost file would store a synchronized copy of your mailbox information(all emails, calendar data, contacts, and tasks) , so the attachments in message are also stored there, here is a similar thread, for you reference: Where are attachments stored?

If they are stored in .ost file, then can we control whether attachments will go into .ost file or not? Will it reduce size of the .ost file?

As I know, we could set what items downloaded to ost file via Synchronization Filters in Outlook(right-click the folder>Synchronization>Filter) , but there may be no option that could manage attachment , for your requirement of reducing .ost file, it's recommended to shorten the date of the Synchronization like below (File>Account settings>Account settings>drag the sync slider to a shorter time, such as 1 week)
129763-image.png

Hope that would be helpful to you.


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