When messages are deleted in Outlook Express, they are not actually removed from the database containing your e-mail data. Rather, the messages are marked to let Outlook Express know that they can be removed the next time the database is compacted. Compacting the message store is necessary for Outlook Express to maintain a reasonable database size and avoid file corruption. Because it is necessary, Outlook Express offers to compact your message store every 100 times the program is used. If you do not compact your message store, the message will continue appearing. Compact the Outlook Express message store manually to remove the message asking if you would like your message store compacted automatically.
Launch Outlook Express. Click "File," then click "Work Offline." This disconnects Outlook Express from the Internet temporarily, ensuring that the message store is not in use while you are compacting the database.
Note: If you do not want to compact the Outlook Express message store at all, see Section 2.
Click "Tools" and then "Options."
Click the "Maintenance" tab.
Click the "Clean Up Now" button.
Click the "Compact" button. This process may take some time depending on when the message store was last compacted.
Click "Close" or "OK" to close each window. The offer to compact the Outlook Express message store automatically will no longer be displayed. Click "File" and "Work Offline" to reconnect Outlook Express to the Internet. Compact the message store periodically to prevent the message from being displayed again.
Press the Windows logo and "R" keys to display the "Run" dialogue box. Type "regedit" without quotation marks into the box and press "Enter." This opens the Windows registry editor.
Click the plus icons on the left side of the folder tree to navigate to "HKEY_CURRENT_USER," "Identities," "(long string of letters and numbers)," "Software," "Microsoft" and "Outlook Express" folders.
Click the "5.0" folder under the "Outlook Express" folder.
Find the value named "Compact Check Count" on the right side of the window and double click it.
Change the number displayed under "Value data" to "0" and click "OK." Close the registry editor. Outlook Express will not offer to compact your message store again until it has been launched another 100 times.
Although it is possible to turn off the offer from Outlook Express to compact your message store by making the registry edit described in this article, it is strongly recommended that you compact your message store instead. Failure to compact the message store periodically may lead to file corruption and data loss.