Conflicts happen when a copy of an item stored on your email server is out of sync with a copy of an item stored on your local computer. Occasionally, Outlook will store conflicted items in a folder called Conflicts. The tool provides a button to view the size of your Deleted Items folder and empty your Deleted Items folder. Often, the cause of a large mailbox is a large Deleted Items folder.

This tool can also help you search for older or very large messages that you might want to delete or move to an Outlook Data File (.pst). You can use the Mailbox Cleanup tool to view the size of your mailbox and individual folders. There are several ways to reduce your mailbox size. To reduce the size of your Outlook Data File (.pst) or Offline Outlook Data File (.ost), you can manually compact the data file. Select your version of Outlook below to see instructions on how to reduce the size of a. If you use an Microsoft 365, Exchange, IMAP, or account, a copy of your mailbox is stored in an Offline Outlook Data File (.ost). Note: If you use a POP account, all of your email account information, including your folders, email messages, contacts, calendar, and task information is stored in an Outlook Data File (.pst). If you receive a message that your mailbox is over its size limit, deleting messages and folders can help, but if you store your information in an Outlook Data File (.pst) or Offline Outlook Data File (.ost), that data file may not shrink in size automatically. Large mailboxes can take longer to open and search, and many email providers, including Microsoft 365, limit the maximum size of your mailbox. The more email you send and receive, the larger your Outlook mailbox can grow.

Office 2016 cleanup tool