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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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John Hurst earned 500 total points
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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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by:Andrew Hancock (VMware vExpert / EE MVE)
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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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by:John Hurst
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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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by:Andrew Hancock (VMware vExpert / EE MVE)
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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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by:John Hurst
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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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by:Andrew Hancock (VMware vExpert / EE MVE)
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what a PITA.

New install of Outlook I think is needed.
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by:John Hurst
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Yes. I do not think a new install of Outlook with aid the compatibility issue with the old OST, though.
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by:Andrew Hancock (VMware vExpert / EE MVE)
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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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by:Clark Kent
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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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by:John Hurst
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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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by:Andrew Hancock (VMware vExpert / EE MVE)
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@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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by:Kev Tom
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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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by:Lisa Miller
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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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by:Andrew Hancock (VMware vExpert / EE MVE)
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Yes, I know that.

My issue is keeping the existing contents, rather than syncing all again!
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by:Kev Tom
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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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by:John Hurst
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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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by:Andrew Hancock (VMware vExpert / EE MVE)
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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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by:Andrew Hancock (VMware vExpert / EE MVE)
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what is rather strange is Outlook is not crashing yet, although OST > 20GB!
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by:John Hurst
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Thanks for the update. I am not sure about your last statement if this is the Outlook 2007 client.
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by:Andrew Hancock (VMware vExpert / EE MVE)
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it is Outlook 2007!

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

time will tell.
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