Maximum Outlook PST file size in Windows 7

What is the Maximum Outlook PST file size in Windows 7?

August 4, 2011 -- I was asked recently if there is a maximum size for the PST (Personal Storage Table) file in Microsoft Outlook (the email component in some versions of Microsoft Office) while running under Windows 7. Actually, the question is phrased incorrectly, as the issue relates to the version of Microsoft Outlook in use, rather than the version of Windows.

Let me summarize the file size limits for the different versions of Outlook. These rules apply equally to PST files and OST (Offline Storage Table) files which are used in conjunction with Microsoft Exchange. Most home and small business users will only see PST files.

For Outlook 97, Outlook 2000 and Outlook 2002 (Office XP) there was a fixed limit of 2GB per PST file. This is not expandable. Outlook will let you exceed this size limit and then refuse to open.

Outlook 2003 and 2007 had a default limit of 20GB per PST file. Outlook 2010 increased the default size limit to 50GB.

However, to support the new size limits the file has to be in UNICODE format, which is the default for PST files created in Outlook 2003 and later. For Outlook 2002 and earlier, the ANSI format was used. These file formats are not compatible with each other, but since Outlook 2003, Outlook could use either file format. What this also means is that moving an old ANSI Outlook file forward to a new Outlook version would still face a restriction of 2GB.

Thus, if you started out using Outlook 2000 under Windows XP, and possibly upgraded once or twice since then, and recently moved up to a new Windows 7 computer with Office 2010 and Outlook 2010, you could still find yourself with an old ANSI format PST file and a size restriction of 2GB.


How do I know what format my PST is in?

In Outlook 2003, for example, you can check which format is being used by selecting File > Data File Management > double-click the PST file. In Outlook 2010, select File > Account Settings > Data Files > double-click the PST file. In any version of Outlook, if the Format field shows (97-2002) it is in ANSI format, otherwise it is in UNICODE format.

See the examples below looking at two different PST files in Outlook 2010 under Windows 7. This first illustration shows a PST file brought forward from Outlook 2003 which had originally been created in Outlook 2000. This file is in ANSI format and thus faces a 2GB size limit.

This second illustration shows a newly created PST file in the same Outlook 2010. We know this file is in UNICODE format since it doesn't indicate "Outlook Data File (97-2002)". Since this particular file was created in Outlook 2010, by default it will have a file size maximum of 50GB. I say "default" because it is a setting which can be changed. The theoretical maximum size can be almost 4TB, but I would recommend evaluating your Outlook folder structure and archiving rules if you find yourself approaching the defaults.

Reorganizing or repairing extremely large PST files will be painful if things go wrong (which they can and do). The size defaults can be modified through the Group Policy Editor or via Registry changes. Follow the link to "Increase maximum size pst-files" if you find yourself bound by the defaults.

The procedure for converting a PST file from ANSI to UNICODE is faily simple. In basic steps, you open Outlook (with your exisiting ANSI PST file) and then create a new PST file, which in Outlook 2003 and later will be created in the UNICODE format. Then you copy all of your mail folders from the ANSI PST file to your newly created UNICODE PST file. After that, you set the new file as the default, and finally disconnect the old ANSI file. Follow some excellent instructions in the article "Migrate from ANSI to UNICODE".

For most people who use Outlook, their email is quite important to them. Loss of the entire PST file (which includes Contacts, Calendar, Tasks, and Personal Email Folders) could be quite devastating. Before upgrading your Outlook version or making major changes to your PST file (such as importing email or contacts from other email clients), always do a backup first. Learn where your Outlook PST file is stored, and perhaps move it to a sub-folder in (My) Documents folder, or somewhere that it will be easily backed up with your other documents. I can recommend starting with Safe PST Backup Free Edition as a way of backing up your Outlook PST files automatically on a schedule -- works in the background whether Outlook is running or not.

--MLJ