Are there any other errors in the event log?
Check for the following events:
Check the application log on your Exchange Server for the following:
Event Type: Error
Event Source: MSExchangeIS
Event Category: General
Event ID: 1112
Description: The database "Mailbox Store (Server Name)" has reached the maximum allowed size. Attempting to unmount the database.
Event Type: Warning
Event Source: ESE
Event Category: Space Management
Event ID: 445
Description: Information Store (3160) The database D:\Program Files\Exchsrvr\MDBDATA\pri
v1.edb has reached its maximum size of 16383 MB. If the database cannot be restarted, an offline defragmentation may be performed to reduce its size.
If this is the case then Services Pack 2 can be applied for Exchange Server 2003 from here:
http://www.microsoft.com/DOWNLOADS/details.aspx?familyid=535BEF85-3096-45F8-AA43-60F1F58B3C40&displaylang=enIf you are running Small Business Server 2003 then you need to ensure that you have SP2 for Exchange along with SP2 for Windows and SP1 for SBS:
http://www.microsoft.com/windowsserver2003/sbs/downloads/sp1/default.mspxOnce you are running SP2 for Exchange you can increase the size of your Information Store Limit but following this article:
http://support.microsoft.com/kb/912375 upto a maximum of 75GB