OST vs PST file size

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New Member
Outlook version
Outlook 2010 64 bit
Email Account
Outlook.com (as MS Exchange)
I need to archive and then recombine some email data files for a client. I am noticing a large size difference between the current OST files they are using and the PST files I create if I do an export from those accounts. (eg 5G for OST and 2.4G for resulting PST). Is this large a size difference something to be concerned about?

The client has made a complete mess of the data by somehow partially importing other data files and using more than one account in the same profile. I am trying to sort this out and need to export piecemeal from all involved datafiles to try and recombine thiings into one file for archiving. I am concerned that I may be missing something if I just assume the small PST file mirrors the parent OST file given the size difference.


New Member
Outlook version
Outlook 2013 32 bit
Email Account
Sadly, a PST or OST file doesn't reflect the real data well. If I fill either files with 5GB of data, then delete 4GB, the files is still 5GB.
You have to either compact it, or inside Outlook, see the folder size properties.

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