Microsoft Outlook Mail is widely used by most businesses, and has been for many years. When it is used in conjunction with a Microsoft Exchange Server, your email messages, calendar, tasks, and other items are either saved on a mail server, on your computer, or both.
Offline Outlook Data File (.ost)
If you are using a Microsoft Exchange account, your items are usually delivered to and saved on the mail server. Outlook is setup to create a local copy of your mailbox in an (.ost) file to allow you to work with your messages even when you can’t connect to the mail server.
Outlook Data Files (.ost) are used when you have an Exchange account and want to work offline or use the default Cached Exchange Mode. This type of data file is also used for accounts that you set up with the Outlook Connector for Outlook.com (formerly Hotmail). Outlook (.ost) files are always copies of items that are saved on a mail server and don’t have to be backed up like Outlook (.pst) files. The .ost file is updated with the Exchange server when a connection is available. This process is known as synchronizing folders.
You can add, delete, and change the contents of an offline folder exactly as you can for a folder on a server. For example, you can change and move items between folders, send messages that are included in your offline Outbox, and view the contents of your offline public folders. Meanwhile, new messages are kept in your Inbox on the server, and other people might add, delete, and change items in public folders. You’ll not be aware of these changes on the server until you synchronize. You work with the information offline on your computer, and Outlook synchronizes the information with the server. When your connection to the Exchange computer is interrupted, you can continue to work with your data. When a connection is restored, changes are automatically synchronized, and the folders and items on the server and on your computer are identical again.
Outlook Data Personal folder File (.pst)
Outlook (.pst) files are used for POP3, IMAP, and web-based mail accounts. When you want to create archives or back up your Outlook folders and items locally onto your computer.
This is the most common file in which information in Outlook is saved by home users or in small organizations. Home users usually use an Internet service provider (ISP) to connect to the Internet. The ISP also provides one or more email accounts. The most common types of accounts are referred to by their Internet protocol names — POP3 and IMAP. Another type of account is an HTTP or web-based account that works similar to IMAP email accounts. All three account types use a .pst file.
Your online Exchange server items can also be moved or archived to an Outlook Data File (.pst), and because a .pst file is kept locally on your computer, it is not subject to mailbox size limits on the mail server. By moving items to a .pst file on your computer, you can free up storage space in the mailbox on your mail server. Outlook can be configured to deliver new items to a .pst file, but if you do this, it has several disadvantages. This includes being unable to work with your items when you are using Microsoft Outlook Web Access with the Exchange Server email account or when you are working on another computer. You can save, copy, and move a data file (other than the file that is used as your default delivery location) to another location on your computer or to a share on the network. However, you must have folder read/write permissions to open an Outlook Data File (.pst).
Warning: Do not access an Outlook Data File (.pst) from a network share or another computer, because it increases the possibility of data loss due potential file corruption. This is only an issue with .pst files, and not .ost files because if an .ost file becomes corrupt, you simply delete it and re-build another one by caching the online mailbox to create a new .ost file, no data is lost as the mail items are always on the online server.
Tip: You should regularly back up your Outlook Data Files (.pst) and save them in a safe place. Your ISP or Microsoft can’t recover your e-mail or other items if the file is lost.
Outlook Data file Best Practices
To ensure that your mailbox does not run into problems with performance issues and data corruption it is important to maintain your mailbox and practice good housekeeping habits. When your Outlook data files become too large it creates the potential for bigger problems. Online storage space of your mail servers is not unlimited and you may reach your mailbox quota which could prevent you from sending and/or receiving emails if your mailbox is not cleaned up regularly. Pro-actively archive old mail to a PST file, and store the file safe backup location to access only when needed. Be conscious of the size of the PST files you are creating. If they are getting too large, you may need to create smaller separate ones. Where you store them could also be a problem if they are too large, ensure your storage is formatted to accept files larger than 4GB which is the limit of Fat32 formatted devices. In general try to keep PST files under 10GB to reduce the risk of corruption and data loss. PST files can sometimes be repaired, but not always, so keep extra backups of important PST files.
Remember to empty your deleted items, and spam folders before creating PST files if you plan on creating a backup of your entire mailbox. If you have 10GB of deleted items and 5GB of Spam, it is going to increase the size of the PST file and the time it takes to create it. The less unnecessary files, the less likely that they will contribute to possible data corruption as well. No one needs to have a 35GB mailbox. Large mailboxes can also lead to performance issues, especially when the entire mailbox needs to be downloaded to create new OST files.
Keeping your mailbox clean and reducing your OST and PST file sizes will save space on your hard drive as well. Several PST files and a few large OST files could quickly eat up all your free space which in turn will cause other problems from performance issues to errors.
If an OST file becomes corrupt and you need to build another one, remember to delete the old OST file off the hard drive, you cannot use them anymore and will just be eating up your drive space as well. Remember one 10GB mailbox, multiplied by 5 old .ost files becomes 50GB of drive space.
If everyone does their part to keep their mailboxes clean, then there will more available server space for everyone, more local space for yourself and less need to spend more money on larger hard drives, and may even prevent having to call your IT department to resolve related issues caused by size and corruption.
Reference: Introduction to Outlook Data Files (.pst and .ost) at https://support.office.com/en-us/article/Introduction-to-Outlook-Data-Files-pst-and-ost-6d4197ec-1304-4b81-a17d-66d4eef30b78
Paul Comtois is a Client Support Specialist at Triella, a technology consulting company specializing in providing technology audits, planning advice, project management and other CIO-related services to small and medium sized firms. Paul can be reached at 647.426.1004. For additional articles, go to www.triella.com/publications. Triella is a VMware Professional Partner, Microsoft Certified Partner, Citrix Solution Advisor – Silver, Dell Preferred Partner, Authorized Worldox Reseller and a Kaspersky Reseller.
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