It is to most end users’ benefits to have the ability to work in an off-line mode. We frequently see people working away on reports or email while traveling on airplanes or working in places that do not have internet access.

End users have the option to work in an off-line mode while working on their email. They are able to do this because Outlook supports files known as dot OST (.OST) files. These dot OST files are Offline Folder files that allow users to make changes to their email files and then, at a later or more convenient time, synchronize those changes with the Exchange server.

But sometimes they may encounter performance problems when they are working with items in a large dot OST file. One of the problems they may have is that Outlook stops responding or hangs during normal usage. End users will more than likely be in the middle of an email activity such as reading emails, saving emails or deleting emails.

Earlier versions of Outlook, prior to Outlook 2007, did not exhibit these problems. Most often the slow response or no response problems are with very large dot OST files that are greater than four Gigabytes (4GB). Slow response times can be seen during email downloads or during synchronization and will often take longer and longer as the dot OST file continues to increase in size. Administrators should note that the slower the disk speed is then, the more likely it is that the slower response times will be seen.

Microsoft made changes when they introduced Outlook 2007 and some of those changes contributed to the slow response time. One of those changes occurred in how data was written to disk. As the number of items in the dot OST files increased then how often data was being written to the disk drives was also increased. Part of this methodology was meant to accommodate the new data structures of the dot OST files.

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