Some older versions of Outlook still have a limit on how big your Offline Storage Folder (OST files) or Personal Storage Folder (PST files) can get to be. For example, in some Outlook versions, when the OST files or the PST files approach 2 GB, you will get an error message indicating that you cannot add any more data. In fact, at times, when the OST files go beyond the limit, they almost immediately get corrupted and the OST file becomes inaccessible. There is a real danger of losing vital data stored in the OST file and you may need to recover OST data using recovery software.
This problem arises even when you try to synchronize your OST file with the server-based mailbox and your mailbox is larger than 2 GB. Not only does the OST file stop accepting data but even the synchronization process is abruptly stopped and you may get the message, 'Errors in background synchronization. In most cases, more information is available in a synchronization log in the Deleted Items folder.' If you now look up the synchronization log that is stored in the Deleted Items folder, you will find an entry that will suggest to you what the problem is. The message will state amongst other things that the OST file you are trying to use has already reached the maximum allowable size of 2GB. If you would like to continue using this OST file, you will need to immediately reduce the amount of data in the OST file. For this, it is suggested that you immediately go offline and start Outlook in the offline mode. Now carefully go through the items stored in Outlook and permanently delete all those that are no longer needed. This will help in reducing the size of the OST file, make better use of the space available and help recover OST data without any damage.
The other option is to move some of the data contained in the OST file into a PST file. This way too, you can reduce the size of the OST file without having to delete any items stored in Outlook. Either way, you can reduce the size of the OST file ' now compact the folders so that the space can be used more efficiently and then proceed to re-sync the folder.
Since Outlook Offline Storage Folders (OST files) were never expected to grow as large as 2 GB, this limit was thought to be fairly reasonable. Later versions of Outlook have improved on this design and provide much larger limits on the OST file size.
