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There are a few questions on here that come close to answering the questions but never really a definitive answer.

Is there a limit to Mailbox size, email count, and folder count in Outlook 2010 x64 where stability and performance will begin to be compromised? If so, is there documented information from Microsoft that my team can forward to users in our office?

I've had at least half a dozen users come to me with performance issues in Outlook and it's always due to mailbox size.

Here are the details of an .ost I'm looking at right now.

50+ Shared folders

~60,000 emails across the local Inbox, Sent Items, and Deleted Items.

another 30-40k or so emails across the shared folders

.ost total size is ~40GB

Most of our users are working with either Thinkpad T400's (being phased out) or Thinkpad T440p's and T450s' all running Win7 Enterprise x64.

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As shown here in the Microsoft documentation.

By default, Personal Folders (.pst) and offline Outlook Data File (.ost) files are in Unicode format in Microsoft Outlook 2010 and Outlook 2013. The overall size of .pst and .ost files has a preconfigured limit of 50 GB.

That is in 2010 and 2013.

The default .pst and .ost file size limit in Outlook 2007 and in Outlook 2003 is 20 GB.

Now beyond there all I have is anecdotal evidence of stability, performance and other issues with PSTs and Outlook. Using PSTs over a network share used to be frowned upon by Microsoft, but I am not seeing that in the documentation for Outlook 2010+.

  • Using PST files over network shares is still frowned upon in newer versions of Office, though a better word might be "dangerous." Even one microsecond of lost connectivity, or a server that's too slow to dish out data and Outlook will die with sparks and smoke. – I say Reinstate Monica May 26 '17 at 1:48

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