Microsoft’s Outlook email management program stores all user data, including messages, contacts, and calendar entries within a single .pst file called a Personal Folders file. As this file grows, it can start to cause errors within Outlook, including program crashes or data corruption. While backups are an important safeguard against potential data loss, they alone do not adequately circumvent these kinds of errors.
Archiving old or infrequently used data serves to reduce the overall size of the .pst file, and should be done periodically depending upon the volume of email your Outlook program handles. Users who send and receive relatively large amounts of email or frequently deal with files containing large attachments will need to archive more regularly. Typically, Outlook’s performance will begin to be impaired as .pst file sizes exceed 500 MB.
Note: Before beginning the archive process, it is important to backup your current .pst file. A quick backup procedure may be found in our Backing Up Personal Data Files article.
To manually archive data within Microsoft Outlook 2007, take the following steps:
1. Open the File menu, click New and select Outlook Data File.
3. For the purposes of this demonstration, we have named the file „archive“ below. The name of the archive file may be chosen arbitrarily; however, it is important that Personal Folders File is the option that is chosen from the „Save as type:“ drop-down menu. Once the file has been named, click OK to continue.
4. You will be prompted at this point to name the newly created file. This is the simply the title that will appear in the navigation pane of Outlook once the .pst file has been successfully created. If you would like to secure your archived data with a password you may do that within this window also. Here, we have given our file the name „Personal Folders Archive.“ The new folder should now show up in the navigation pane as shown below.
5. You are now able to move email messages out of your main .pst file and into the newly created Archive folder. You may use the drag-and-drop feature to move data from folder to folder or utilize the Move to Folder… option that appears when appropriate files are right clicked. Entire folders may be moved in a similar manner.
Note: Once you have finished moving files to the archive file, it will be necessary to compact your primary .pst file. For more information, see the article „Compacting Your Personal Data File.“ This is very important, because Outlook will not automatically reduce the size of the file after you archive data; you must shrink the file manually using the Compact feature.
Referenced from: Microsoft.com