Viewing IMAP Folder Storage

Regularly monitoring your IMAP email accounts through your email client can provide several benefits for your email service.

Keeping your IMAP storage low could help improve loading times of your email client, prevent large data usage when adding your address to a new mail software or device, or help to reduce costs of your email subscription.

This guide will explain how to view and monitor individual IMAP folder usage for the most popular email clients.

• Mozilla Thunderbird

• Microsoft Outlook

• Apple Mail

Tested in Version 91.10.0

In Thunderbird, from the Top Menu select View, Layout then Folder Pane Columns.

If you don’t have the Top Menu Enabled

You can instead use the Menu Stack/Burger icon (three horizontal lines) in the top right-hand corner to see the View, Layout, Folder Pane options.

The new column that appears will provide options to show the total number of messages, the number of unread messages, and the size of the folder.

For the purposes of this guide we are only interested in the Size of the Folder.

To enable this view, click on the tiny icon at the top of the folder pane - it looks like a little table with a downward pointing triangle - and click the Size menu option.

This will update the column to display the Folder Size, as above. Fields with arrows indicate sub-folders within the parent folder. Sizes will be displayed in kB, MB and GB.

You can now use this information to manage storage for your individual IMAP folders.

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Microsoft 365, Outlook 2021, Outlook 2019, Outlook 2016 & Outlook 2013

With your Outlook program open, navigate to the main Mail view, then click your account to highlight it. Next, select Folder then Folder Properties from the top menu. 

On the Properties window that opens, click Folder Size towards the bottom. This will open a new window, headed Folder Size.

This window will show the size for each subfolder connected with your account. Each folder size is indicated in kilobytes (KB).

There are many online tools available for converting large KB numbers into something more readable, but a quick method is to move the decimal point over three places to the left.

For example, 4742 KB is roughly 4.7 MB.

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Firstly open the Mail app on your Apple Device. Once opened, in the Mail sidebar, Ctrl+click (or right-click) the Inbox, then choose Get Account Info.

In the Account Info window that opens, click the Account drop-down menu, then choose an account.

If you only have one account within Mail, this list will be short.

Click Quota Limits to view details about your account. The window should display details on the size and number of messages within your various IMAP folders. Sizes will be displayed in kB, MB and GB.

Clicking a folder then Show Messages opens that folder in new window, allowing you to remove/archive any messages you no longer require.