Archive older items – Archive old items that you want to keep, in order to stay within the recommended storage threshold. For example, if your mailbox has only 1GB of storage, then move the old items that you want to keep to a PST archive. If your mailbox has 50GB of storage, move your old items in the cloud. Note: If your mailbox has only 1GB of storage, then it means that it has not been migrated to Exchange Online. In this case, when your mailbox reaches its upper limit, your administrator might start limiting functionality. For example, at 900 MB you might get a warning, at 1024 MB you might be unable to send email, and at 1300 MB you might be unable to receive email.If your mailbox has 50GB of storage, then it means that it has been migrated to the cloud. Empty the Deleted Items folder – Empty the Deleted Items folder frequently to make sure you aren’t keeping messages you don’t need.Empty the Junk Email folder – Periodically empty the Junk Email folder to save your inbox space for messages you actually want.Store attachments outside your mailbox – As attachments accumulate over time, they can take up a lot of space. If you want to keep attachments, consider saving them to BOX, or to folders on your computer.Use the Mailbox Cleanup tool - Are you getting weekly or even daily messages warning that you are about to run out of mailbox space? Mailbox Cleanup is a one-stop-clean-up tool you can use to trim the size of your mailbox. See how to Use the Mailbox Cleanup tool.