Outlook Mailbox Cleanup

The best place to start is to open the Outlook Mailbox Cleanup tool.

In Outlook, choose File > Info > Cleanup Tools > Mailbox Cleanup.

First, choose the View Mailbox Size option, which scans the size of your mailbox and all of the subfolders.

This is a great way to target which folders are the biggest contributors to your large mailbox so you can clean these up first.

When connecting to your Exchange server, you’ll see a Local Data and Server Data tab.

Only look at the Local Data tab; cleanup changes you make will automatically take place on the server as well.

Next, pick the options to Find older or larger items that you can delete directly from the results to reduce the Outlook mailbox size.

Depending on your archive settings (see Archive Older Messages below), you can also run an AutoArchive.

Finally, check the size of the  folder and Empty the Deleted Items folder if you want (specific options are detailed below as well).

Depending on your version of Outlook, one option is to view and delete multiple versions of items in our mailbox.

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Move Messages to Your Personal Folders

If you’re accessing Outlook from an Exchange server, another way to reduce the Outlook mailbox size is to move Outlook items to your Personal Folders.

Please note that this option may not be available to you as many organizations have moved away from supporting Personal Folders.

Even though the messages you move to Personal Folders are no longer counted in the size of your mailbox, the Personal Folders file (outlook.pst) is stored on your local hard drive and is not accessible remotely.

You should also backup this file to prevent losing these Outlook items if your computer goes down or is updated.

If you are running a standalone version of Outlook, your email, calendar, tasks, and notes are all stored in the outlook.pst file (or .ost file-offline), which has a size limit of 50GB (for Outlook 2021, 2019, & 2016).

Archive Older Messages

Another useful maintenance step is to periodically archive your Outlook folders. If you are accessing Outlook from Exchange, you may not be able to change archive options as archiving is often controlled by system administrators or a third-party program.

Setup your archive preferences under the Info > Cleanup Tools > Archive option.

The archive.pst file can be created and updated at any location you specify, usually your local hard drive.

Archived items are removed from your Outlook mailbox size and moved to the archive file based on the settings you determine.

Just as with the Personal Folders file, your archived items are not accessible remotely; the file should be backed up on a regular basis.

Empty Deleted Items

Quickly clean up your deleted items by automatically emptying the Deleted Items folder when you exit Outlook.

To apply this option choose File > Options > Advanced tab. From the Outlook start and exit option, check Empty Deleted Items folder when exiting Outlook and OK to apply.

To manually clear deleted items, locate and right-click the Deleted Items folder and click Empty Folder on the shortcut menu (Empty “Deleted Items” Folder for Outlook 2010). Once you clear deleted items, it cannot be reversed. If you feel confident that you want to delete a message forever, you can bypass the Deleted Items folder by pressing [Shift] + [Delete] for a selected item instead of pressing the [Delete] key. Then confirm the delete process.

Save and Remove Attachments

Attachments in email messages are responsible for the bulk of the space used in your Outlook mailbox.

Depending on the email communication, one option is to save the attachment and then remove the attachment from the original message. This requires extra steps yet may help slim down the size of your Outlook mailbox:

1. Open the message.

2. Right-click on the attachment and then pick Save All Attachments. Or select Actions from the Message tab. Then pick Other Actions > Save All Attachments.

3. Next, locate and select the folder where you want to save the file(s) and pick Save.

4. Once you have saved the attachment, delete the message if it doesn’t need to be retained. If you need to keep the message, you can remove attachments from a message by right-clicking them and choosing Remove.

Bonus: Reduce the Size of an Outlook Data File (.pst)

Note: This tip only applies to Outlook running on a stand-alone computer.

If you delete items from an Outlook Data File (.pst), the file is automatically compacted in the background when you’re not using your computer and Outlook is running.

You can also manually start the compact command immediately. It will likely take several minutes to compact an Outlook Data File (.pst).

1. Following the steps above, delete any items that you do not want to keep and empty the Deleted Items folder.

2. Click the File tab.

3. Click Account Settings, and then click Account Settings.

4. On the Data Files tab, click the data file that you want to compact, and then click Settings.

5. Click Compact Now.

NOTE:  You do not have to exit Outlook after you compact an Outlook Data File (.pst) file.