Understanding PST file size limitations – ANSI vs Unicode
This is an article that really applies to those who have been using Outlook since the days of Outlook ‘2000 and have migrated .pdt data files as they’ve upgraded to newer versions along the way (i.e. to ‘2003 / ‘2007 / ‘2010) and have or are moving to the latest version of Office 365 (i.e. ‘2013 & ‘2016).
Since Outlook ‘2003, new PST files that were created by Outlook are Unicode PST files which have a capacity of up to 50gb. However, PST files that have been migrated from Outlook ‘2002 (XP) were originally created as ANSI PST files that have a size limitation of 2gb regardless of what version of Outlook they are used in.
How to tell if a pst file is ANSI or Unicode?
- right-click on the root of the PST file
- select Data File Properties –> click on the Advanced button in the window that appears
- if the File format description shows (97-2002) in the description, it is an old format ANSI PST file
While Outlook ‘2013/’2016 supports the use of ANSI based PST files, it is highly recommended that the PST file first be converted to the Unicode format before being used in ‘2013/’2016. The reason for this is that OL’2013/’2016 can encounter issues reading an old ANSI based pst file for the first time especially if there are errors contained in the file. This should be done using the Outlook version in use (i.e. ‘2010 or earlier) using the following steps
- With Outlook closed, locate the PST file and run ScanPST on the file to eliminate any errors that may exist You may need to run ScanPST multiple times to eliminate all errors
- once the file has passed through the ScanPST process, open Outlook and do a PST2PST export which will automatically create a new Unicode based PST file. It is the exported PST file that should be used in Outlook ‘2013/’2016 to avoid potential problems
If you do not have access to the old version of Outlook (version in use prior to migrating to ‘2013/’2016), then ScanPST should be run on the PST file before opening it in Outlook. Once done, open Outlook and perform a PST2PST export of the PST file to create a Unicode version of the file. When the file has been exported, you will need to add it to the Outlook profile manually, one series of steps to perform this process is
- with Outlook closed, open the Control Panel <Mail> app
- click on the Data Files button –> Add the newly exported file to the profile
- if there are POP3 accounts associated with the old PST file, then click on the Email tab, highlight the POP3 account and at the bottom of that screen, change the destination to the <Inbox> contained in the newly added pst file
- when all POP3 accounts are changed accordingly (if applicable) then return to the Data Files list and remove the old ANSI based PST file
The same steps can also be accomplished from within Outlook by going to File –> Account Settings.
Category: Troubleshooting, Understanding Outlook
