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The size of an Exchange mailbox keeps growing with the inflow of messages/ message attachments, and the addition of contacts, notes, calendar entries, and so on. Gradually, the size of the mailbox reaches a saturation point where it becomes difficult for users to manage extensive data. It not only affects the performance of Exchange but also increases the chances of data corruption. Fortunately, Exchange administrators can put a limit on the size of the mailbox sizes by setting a quota in various parameters.

Manage Exchange Mailbox Storage Limits

The Storage Limits for an Exchange mailbox specifies a limit where the user will get a warning and a limit where the message flow stops.

  1. Login to Exchange Admin Center and follow Servers>>Databases. Select any database and double-click it.
  2. Go to the Limits tab and here you can set the following limits –
    • Issue a Warning at (GB)
    • Input a value for the database size and Exchange will provide a warning when it reaches the size.

    • Prohibit send at (GB)
    • The Exchange will prohibit the user from sending a message when it reaches the limit you specify here.

    • Prohibit send and receive at (GB)
    • The Exchange will prohibit the mailbox from both sending or receiving messages when it reaches the value you entered here.

    • Keep deleted items for (days)
    • The Exchange will keep the deleted items for the number of days you mention here.

    • Keep deleted mailboxes for (days)
    • The Exchange will keep the deleted mailboxes for the number of days you mention here.

  3. Click Save, and the changes will apply immediately.

Read Also : Various email limits in Exchange Online (Office 365)

How can end users manage the size of mailboxes?

There are different ways in which end users can manage the size of their mailboxes. Here, we will discuss them too.

Move Messages to PST Files

If you do not want to delete your information stored in the mailbox but want to reduce the mailbox size, then you can move data from the mailbox to a PST file. You can select the lesser important messages and keep them in a PST file. The benefit of this is that it keeps the files saved at a local drive rather than on the Exchange Server. So, it reduces the mailbox size without deleting the data. Here is the simple procedure to create a Personal Folder in Outlook;

  1. Start Outlook and follow File>>Account Settings>>Account Settings>>Data Files.
  2. Click the Add button. Provide a new name to the file and browse the location to store it.(the default location will be C:\Users\username\Documents\Outlook Files.
  3. As soon as you create a new personal folder (PST file), It will show in Outlook, and you can save your messages over here.

Also, you can use an efficient EDB to PST converter to export Exchange mailboxes to PST. Professional EDB to PST converters provide PST a splitting option by which you can save large Exchange mailboxes to multiple PST files.

Enable Auto-archive in Outlook

Enabling auto-archive in Outlook is highly efficient in reducing the mailbox size as it downloads the messages and saves them in the archive folder. Let’s see its process;

  1. Start Outlook and follow File>>Options>>Advanced>>Auto Archive.
  2. Click the Auto-Archive Settings button and set various options based on your archiving needs. Also, browse a location where you want to save the archive file.
Reduce the size of OST file

Another way to reduce the size OST file is using the compact option of Outlook. Here are the steps;

  1. Empty the Deleted Items folder.
  2. Follow File>>Account Settings>>Account Settings>>Data Files.
  3. Select the Data File which you need to compact and click the Settings button.
  4. Click the Compact Now option and click OK.

Using these techniques, you can effectively reduce the size of the Exchange mailbox and improve its performance.

Apart from setting the size limits and reducing the mailbox sizes, there are many things Exchange administrators can do to ensure the best performance of Exchange Server. However, for this, you need minute details regarding the functioning of the entire Exchange environment. That’s why you should go for a reporting software which records all activities of Exchange and brings the information in a format which you understand easily. Kernel Exchange Reporter is a simple tool that can help you in this regard.

Once you have an understanding of the size of Exchange mailboxes, you can use Kernel for Exchange Server Recovery to export Exchange data or to import data to Exchange. Also, it helps you perform various Exchange tasks like Exchange recovery, Exchange migrations, and cloud migrations.


Kernel Exchange Reporter is an analysis and reporting software which checks the activities of Exchange and prepares various charts and reports. You can use the software to check the mail flow of any mailbox and see if its size is increasing. So, you can easily get details of all the mailboxes and accordingly, optimize and plan your infrastructure and environment. For managing the Exchange environment effectively, you can use Kernel for Exchange Server too.

Kernel Exchange Reporter
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