How to Compress an Exchange Mailbox

by Jeff Kaleth

Exchange mailbox compression is done on an information store level in Exchange Server 2003 through a defragmentation maintenance task. This type of activity is a critical part of managing your Exchange environment. Without this type of management, users will start to see performance degradation, and you will possibly receive an increasing number of calls to the help desk.


In Exchange System Manager, right-click the information store that you want to defragment. Click "Dismount Store."


Open a command prompt on your Exchange server.


Browse to the "Exchsrvr/Bin" folder.


Launch Eseutil. This is an Exchange utility used to defragment, repair and test the integrity of the Exchange database. Eseutil defragments the Exchange database by creating a new database. The best method is to defragment the Exchange database with the option that copies it to a separate location. This keeps the original Exchange database in tact. To run defragmentation, use:

"eseutil /d Database_Name /p"

Database_Name is the file name of the database.


  • check Exchange database defragmentation increases efficiency by reorganizing objects; however, it does not change the size of the database. To decrease database size, asking users to delete unwanted email and enforcing a mailbox size policy are best methods.


  • close Dismounting an information store makes it unavailable to users. Make sure you run Exchange defragmentation off-hours.

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About the Author

Jeff Kaleth has been working as a corporate technical writer and computer engineer since 2008. He has experience developing procedural and task documentation, as well as translating technical needs into end-user documentation. Kaleth holds a Bachelor of Science in business administration from Indiana University.

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  • photo_camera Server world image by Satan from