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Exchange Database Size Limit Exceeded – Errors with Solutions

Published By Mohit Jha
Tej Pratap Shukla
Approved By Tej Pratap Shukla
Published On March 19th, 2024
Reading Time 6 Minutes Reading

While working on Microsoft Exchange Server, we often encounter the error message “Exchange Database Size Limit is Exceeded” which leads to a dismounted Exchange database. The problem is the same for all versions of Exchange Server (e.g. users get errors like “Exchange 2003 database has reached its maximum size limit” which is 16 GB or 18 GB depending on the edition).

In this post, we will go through the error and point out the best possible solutions for the problem that arises due to crossing the limitation of Exchange Server size limit.

Problem Overview of Exchange Database Reached Maximum Size Limit

While working on Exchange Server, we came across the term “Logical Size” of the database; which is equal to the sum of the physical size of the EDB and STM databases except for 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 files is greater than or bigger than the size of the default configured database.

The PHYSICAL size of the database never shrinks automatically without intervention from the administrator. When the contents of the database (emails, contacts, attachments, and other items) are removed then the Exchange server marks that space as white space. This white space is first used for new content before increasing the physical size of the database.

Problems of Exchange Database Size Limit Exceeded

Whenever the size limit of the Exchange server database (logical size of database) is about to cross the default size limit or the configured size, you may encounter the following error which will finally lead to the Exchange database being 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 from trying to insert more data into the mailbox store database than the default or configured size limit of Exchange Server.

Solution to Exchange Server Database Dismounted Problem

If you encounter this error in Microsoft Exchange Server which says that the Exchange database size limit is exceeded and the database will be dismounted then, you need to make the quick and right decision before the database becomes useless and corrupted.

Below are the best possible solutions that you can try out for resolving the issue of database dismounting issues. The techniques apply to all the versions of the Exchange Server and are tested by our expert team.

Solution 1: Create a New Database and Move the Content in the Database

You can create a new database and try moving the content of the 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 in improved performance. If this method doesn’t work then please move to the next section.

Solution 2: Change Registry Settings Value to Increase Exchange Database Size

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.

Limitations of Regedit Method for Increasing the Size Limit of Database

The Registry editing method for increasing the database size can cause serious problems (system failure). So it is not recommended to change the registry setting if you are 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 changing the size limit.

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

What’s the Solution If Regedit Fails to Increase the Database Size?

So, these are the best solution that resolves the issues of the Exchange database size limit exceeded problem. If the above two methods fail to repair the EDB file and you still get the database dismounted error then you need to convert your EDB file into PST. You can download the EDB Converter which supports both offline / dismounted Exchange database file.

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This utility provides Quick & Advance scan option to recover & repair corrupt Exchange mailbox as well as .edb files without any loss of data. After recovery, users can easily restore Exchange database to different server in a simplified manner.

Bringing It All Together

Now users have detailed information to resolve the Exchange database size limit exceeded issue. They can either increase the mailbox database or reduce the Exchange database size in Microsoft Exchange. You can use the procedure to resolve the storage problem. Even if the problem remains, convert the offline/dismounted Exchange database file to PST by using the automated wizard. 

Frequently Asked Questions

Q1. What is the maximum size limit of the Exchange 2016 database?

Ans – It is 16 GB only, after that you need to expand it.

Q2. How to open Registry settings in Windows OS?

Ans – To open registry settings, press the Windows+R button and type regedit.

Q3. What to do if Regedit fails to resolve the Exchange database size limit issue?

Ans – You can use the above-mentioned reliable automated tool to resolve the error without hassle.


By Mohit Jha

Mohit is a Microsoft-certified expert who has assisted thousands of clients with Outlook & Microsoft Office 365 issues. He enjoys writing on email clients as well as data migration. He is always excited about giving troubled readers the most up-to-date knowledge, explanation, and refinements.