Exchange Database Reached Maximum Size Error Solution

Mike Keen | May 20th, 2015 | Exchange Server

While working on Microsoft Exchange Server we often encounter the problem of or Exchange Database Reached Maximum Size limit which leads to Exchange database dismounted. The problem is same for all versions of Exchange Server (e.g. you got errors like “Exchange 2003 database has reached its maximum size limit” which is 16 GB or 18 GB depends on the edition). In this post we go through the errors and point out best possible solutions for the problem which arises due to crossing the limitation of Exchange Server size limit.

Problem Overview of Exchange Database Reached Size Limit

While working on Exchange Server we came across the word logical size of the database which is equal to the sum of physical size of the edb and stm database except the logical free space in those databases. The logical size of a database is approaching the limit error means that the size of your edb+stm is greater than or bigger than the size of default configured database. The PHYSICAL size of the database never shrinks automatically without intervention from the administrator. When the contents of database (emails, contacts, attachments and other items) are removed then the Exchange server marks that space aswhite space. This whitespace is used first for new content before increasing the physical size of the database.

Problem of exchange store database size exceeded

Whenever the size limit of exchange server database (logical size of database) tries to cross the default size limit or the one that you have configured you may encounter the following error which will finally lead to exchange database dismounted.

Exchange store ‘<storage group name>’: The logical size of this database (the logical size equals the physical size of the .edb file and the .stm file minus the logical free space in each) is <number> GB. This database size has exceeded the size limit of <number> GB.This database will be dismounted immediately.


The database “Mailbox Store (Server Name)” has reached the maximum allowed size. Attempting to unmount the database. 


Exchange – This database size is approaching the size limit of <some number> GB

As soon as the mailbox store database has reached the maximum size limit, the Messaging Database (MDB) shuts down automatically. In addition to that the MDB will not restart.

This technique is designed to prevent the exchange users trying to insert more data into the mailbox store database than the default or configured size limit of Exchange Server.

Exchange Server Size Limit for Different Versions of Exchange Server

The different versions and editions of Exchange Server like Exchange Server 2003 to Exchange Server 2013 have different default configuration size limit that you can increase by changing registry setting [discussed later].


Solution to the problem of Database Dismounted Problem

If you encounter the error in Microsoft Exchange Server which says that exchange database has exceeded size limit and the database will be dismounted then you need to take quick and right decision before the database is totally useless and corrupt.
Below are the best possible solutions that you can try out for resolving the issue of database dismounting issues. The technique is applicable for all the version of Exchange Server and tested.

Solution 1: Create a New Database and move the content into this.

You can create a new database and try moving the content of oversized database into this newly created database. The benefit of doing this you get free space and it also cleans up the corrupt items resulting improved performance. If this method doesn’t work then please move to next section.

Solution 2: Change Registry settings value to increase the configured size limit of Exchange

Open the registry settings in your system using Start>> Run >> Regedit and browse to the following Registry key
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\<Server Name>\Private-<database GUID>
If the key “Database Size Limit in GB” DWORD exists under the subkey “Private-[database GUID]”then make changes in its value to the desired size in gigabytes or terabytes according to your need. Also make sure to select ‘decimal’ when you enter the number.

In case the “Database Size Limit in GB” DWORD does not then create one and set its decimal value to the desired size in gigabytes.
For changes to be made you may need to restart the information store service for the changes to take effect.

Limitation of Regedit method for increasing the size limit of Database

The Registry editing method for increasing the database size can cause serious problem (system failure). So it is not recommended to change the registry setting if you not 100% sure what you are doing. Also take a backup of your data first before making any changes. Below are the limitations of the above explained methods of chaning the size limit

  • Deleting emails won’t make any difference in the size of database.
  • Improper Registry setting cause overall system failure.
  • Complicated Method which require time and effort and make no guarantee for success.
  • If the database dismounted and run offline then there is no way you can remount using regedit method.

What’s the Solution if Regedit fails to increase the database size?

If anyhow the above two methods fails to repair the edb file and you still get the database dismounted error then you need to convert your EDB file into PST which you can import later. You can download the edb converter which is freely available to resolve the database dismounting issue. So, these are the best solution that really resolves the issues of exchange store database size exceeded problem.