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Outlook for Mac accounts connected to Exchange may sometimes get error messages stating that their Exchange mailbox is full. An IT support team may have to ask the email client users to delete unnecessary emails and attachments or archive their mailbox data. Here, we will go through the causes of this issue and the ways to deal with it. The solution to what Outlook for Mac users can do when their Exchange mailbox is full will be discussed in detail.

Why is the Exchange mailbox full?

An Exchange-connected user mailbox cannot accommodate more messages than the mailbox quota allocated by the Exchange administrator for it. The prominent reasons for the filling of the Exchange mailbox are duplicate items, large-sized emails, and their attachments. The consequences of a bulky Exchange mailbox are corrupted database files, downtime, slow performance, or data loss in severe conditions.

These effects are undesirable, and so, users will have to reduce their mailbox size from the Outlook for Mac email client itself. Deleting unwanted emails and separating attachments from emails can help to some extent. However, a better approach would be to archive the old Outlook for Mac mailbox data and retain only the recent and most relevant items in the mailbox. Let us see how you can check the size of your Outlook for Mac mailbox folders and archive their items.

Instant Solution

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How to check the size of mailbox folders in Outlook for Mac?

In Outlook for Mac, users don’t have the facility to check the size of the entire mailbox. They perform separately for each folder.

You can check the size of the mailbox by following the steps-

  • Right-click the folder
  • Select Folder Properties
  • Move to the Storage tab on the Folder Properties dialogue box.
  • Here you can view the size of the folder as well as the sizes of its subfolders.
How to archive Outlook for Mac mailbox folder data?

The method for archiving folders in Outlook for Mac is given below:

  1. Begin by choosing one or more messages to archive.
  2. From the top ribbon, select Archive.
  3. Click on Continue on the prompt (this will let you create a new archive folder).
  4. Now, to set archiving rules, go to Tools and select Rules, further select Edit Rules.
  5. Then select Exchange from the left menu pane, then click on ‘+’ to add a new rule.
  6. Assign a Rule name and specify the required conditions. Then click on OK to save the rule.
  7. To apply the rule to a folder, select all its emails and click Message > Rules > Apply > Select Rule.
Store Attachments Outside the Mailbox

Always try to save attachments outside the Outlook in a personal folder, hard drive, or disk where it belongs instead of saving them in the Outlook mailbox.

Step 1- Firstly open Outlook and click on the attachment you want to save outside your mailbox.

Step 2- Select the “Save As” option and choose the specific path and location on the hard disk where you want to save the attachment.

Step 3- Now, delete the attachment in Outlook that you save outside your mailbox.

How to backup OLM files to PST?

Many OLM users may want to take a backup of their OLM files in the form of PST files. By doing so, they can access their emails in MS Outlook (Windows environment). This can be done by following a manual or technical solution.

Manual Solution
  1. Launch the Outlook for Mac application. Go to the Outlook menu and then click on Preferences.
  2. Under Tools, select Accounts.
  3. Click on the Add email account option.
  4. Start by signing in to your Gmail account to configure the IMAP email account.
  5. Then configure your Mac Outlook OLM file with the same Gmail account.
  6. Now, create a Gmail label and then start synchronizing the OLM file with IMAP
  7. Now, move all OLM file data to the IMAP account and then move OLM emails from the IMAP mailbox to MS Outlook PST by configuring that IMAP account in the Outlook client application.
Empty the Deleted Items Folder and Junk Email Folder

Another way to reduce mailbox size in Outlook is to empty the deleted items folder and junk email folder. You can quickly get rid of your deleted items by emptying the Deleted Items folder automatically when you quit or exit Outlook. To do so, follow the below steps:

  1. Firstly, open Outlook.
  2. Go to the “Files” > “Options” > “Advanced” tab.
  3. Choose the “Empty Deleted Items folder when exiting Outlook” option from the “Outlook start and exit” option.
  4. Now, click the “OK” button to apply.
Using Outlook Cleanup Tools Feature

You can also use Outlook Cleanup tools features to reduce mailbox size by following steps:

  1. In outlook Go to the File > Info > Cleanup Tools > Mailbox Cleanup.
  2. To execute desired operation, choose “View Mailbox Size“, “Find items older than“, “Find items large than“, “View Deleted items size“, “Empty Deleted Items folder“, “Empty Conflicts“, or “View Conflicts Size“.

By applying this, you can reduce the mailbox size.

Technical Solution

Also, you can opt for a third-party tool, Kernel for OLM to PST converter for the conversion of OLM files to PST. This tool helps you to convert OLM files to PST format. It helps migrate all Outlook for Mac items, including emails, attachments, calendars, etc., to the Windows environment. With this tool, you can also save Outlook for Mac emails to various destinations like Exchange Server, Office 365, Gmail, MBOX file (Apple Mail), etc. For the conversion, you just need to transfer your OLM files to a Windows system with Kernel for OLM to PST. After the conversion to PST, you can access the data in MS Outlook.

It involves a simple procedure-

  • Select the required single or multiple OLM files.
  • Preview the mailbox items existing in the file.
  • Save the file in PST format.


The article focuses on what Outlook for Mac users can do when their Exchange mailbox is full. Some manual practices like archiving, data transfer, or backup are explained; for fully automatic conversion of OLM files to PST, a smart solution is introduced in the end.

Q. What is the maximum email size for Mac mail?

A. The max email size for Mac mail is 20MB. But, with Mail Drop turned on, this limit can be increased up to 5GB for both incoming & outgoing messages.

Q. Why did my Mac stop receiving emails?

A. Your Mac may have stopped receiving emails if your account is offline or disabled. Check to make sure your account is active and connected to the internet. Another possibility is that your mailbox is full, which can prevent new emails from coming in.

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