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OST Compatibility between Outlook 2007 and Outlook 2010, 2012 and later ?

Posted on 2016-07-24
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Last Modified: 2016-08-15
Hi Experts

Does anyone know for definitely the compatibility between OST files, are the standards the same between all versions of Outlook, e.g. 2007 and later 2010, 2013 etc going forward e.g. from 2007 to later, not backwards.

The reason I ask, is we have recently noticed that one of our users, has a offline mailbox size of just under 20GB, and this appears to be the maximum supported for Outlook 2007.

There is a reason we all have offline mailbox, whilst we have no remote access to Exchange, but didn't know there was a maximum limit in Outlook 2007.

So, if we were to upgrade from Outlook 2007 to a later version of office, and reconfigure and use the existing OST file, is it going to carry on as normal, or is it going to download all 20GB mailboxes again?

I'm trying to establish compatibility, and cannot find anything definitive from Microsoft.

We've tried compacting OST file, and despite removing many dead emails, over 20,000 it was made no difference to the sizes on the disks.
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LVL 95

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by:
John Hurst earned 500 total points
ID: 41726549
The size capability keeps moving up. I do not think you can use old OST files with new Outlook. Delete and remake the OST file. That is what we do for clients.

Also the format may have changed in your case (there was a newer format out a while back but it was not obligatory back then.
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LVL 121
ID: 41726553
Thanks John...

The size capability keeps moving up. I do not think you can use old OST files with new Outlook. Delete and remake the OST file. That is what we do for clients.

That's the issue I was afraid of. Unfortunately it will not be possible for them to remote sync 20GB over the internet, where they are located, and it's almost catch-22, if they get to 20GB, Outlook will crash no email.

They are currently offsite for months out of the UK!

I think they will have to install later version of Outlook for new email, and use older version offline, to view old emails, until they get back to the LAN!

There was a free OST viewer, I also saw that may allow them to view emails.
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LVL 95

Expert Comment

by:John Hurst
ID: 41726557
I am not sure about all versions of mail, but I have before turned off Sync so that email is used only online and not cached. Then for the time frame involved, they would not need their OST file.
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LVL 121
ID: 41726569
Umm, this is what happens, when you attach OST from 2007, to 2010!

2016-07-24-16_40_22-Microsoft-Outloo.png
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LVL 95

Expert Comment

by:John Hurst
ID: 41726583
Yes - I have seen that error and the only solution is to remake the OST as the Microsoft error says. Short of not using the OST, I do not know of any other way unfortunately.
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LVL 121
ID: 41726585
what a PITA.

New install of Outlook I think is needed.
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LVL 95

Expert Comment

by:John Hurst
ID: 41726586
Yes. I do not think a new install of Outlook with aid the compatibility issue with the old OST, though.
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LVL 121
ID: 41726608
I didn't mean that, but the end user will be able to use Outlook and connect to Exchange, rather than it crashing at 20GB.

two versions will co-exist side by side, he'll just need not to use the other version to connect to Exchange, at present, until he gets back to LAN, to complete a new Sync, or all mail.
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LVL 10

Expert Comment

by:Clark Kent
ID: 41726609
Hello,
 Similar thread has been discussed earlier. Please refer the link :
https://www.experts-exchange.com/questions/26863616/OST-files-when-upgrading-from-Office-2007-to-Office-2010.html

Hopefully, this will help.

Thanks & Regards,
Clark Kent
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LVL 95

Assisted Solution

by:John Hurst
John Hurst earned 500 total points
ID: 41726611
he'll just need not to use the other version to connect to Exchange, at present, until he gets back to LAN, to complete a new Sync, or all mail.   Yes. That should work.
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LVL 121
ID: 41726616
@Clark Kent Thanks for your post.

when we installed the newer version of Outlook 2010, it created a new OST file it did not attempt to upgrade older version of use the existing ost file, which made us suspicious, it's just annoying Outlook 2007 will crash when it gets to 20GB, not just stop, or give a warning.

only when we forced it to use the old did it complain!

I had read the differences between the versions, but not read anything clearly stated by Microsoft, that the old versions are not compatible going forward. Other than the message, delete it, and it will be recreated, which is not an upgrade. It's just start over again, which wit a 20GB mailbox, sync via Internet, is just  not easily going to happen.
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LVL 2

Expert Comment

by:Kev Tom
ID: 41728797
I'd suggest:
Exporting all the emails to a pst file
Then setup the new version of Outlook and add mail account
Enable cache mode
And then import all the email from the pst file after checking the tick box to not import duplicates.
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LVL 3

Expert Comment

by:Lisa Miller
ID: 41735660
The predefined size limit of ANSI OST file is 2 GB, for UNICODE OST file for Outlook 2007 is 20 GB, and for Outlook 2010 and 2013 is 50 GB.
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LVL 121
ID: 41735679
Yes, I know that.

My issue is keeping the existing contents, rather than syncing all again!
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LVL 2

Expert Comment

by:Kev Tom
ID: 41736898
When you export the existing emails to a pst file and then import it into the new profile then Outlook won't re-download (sync) these emails.
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LVL 95

Expert Comment

by:John Hurst
ID: 41755842
This was a long thread, but did we answer your questions?  I think so.

If not, can you crystalize a single question for us to answer?
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LVL 121
ID: 41755994
We've still not done anything about it at present. but we now understand that OST files are not compatible which was what we found by experimentation.
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LVL 121

Author Closing Comment

by:Andrew Hancock (VMware vExpert / EE MVE^2)
ID: 41755997
what is rather strange is Outlook is not crashing yet, although OST > 20GB!
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LVL 95

Expert Comment

by:John Hurst
ID: 41756169
Thanks for the update. I am not sure about your last statement if this is the Outlook 2007 client.
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LVL 121
ID: 41756256
it is Outlook 2007!

and working above 20GB and not crashing.....

time will tell.
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