View the total size of your mailbox and of individual folders within it.
Find items older than a certain date or larger than a certain size, and then delete those.
View the size of your Deleted Items folder and empty your Deleted Items folder.
Select a message.
Select Sweep from the ribbon.
Choose when and where you want to move email messages from the sender you chose. For example, you can send all messages from that sender to a specific folder (even your trash) for one time or for all future messages.
Select OK to perform the selected action.
Right-click a message and select Create rule.
Choose the folder where you want all messages from that sender or set of senders to be moved, and then select OK.
The rule will be applied to all incoming messages. If you'd like to run the rule on your inbox immediately, select the check box for Run this rule now in Inbox.
Note: Additional Rules customizations are available to help you manage your Outlook messages in a way that makes sense for you.
Select Move to and choose a folder.
Or, select Categorize and choose a category.
Select Delete. Select Archive if you might want it later.
Note: You can also right click on folders and perform bulk actions on those folders. Select Empty, Mark all as read, and Assign policies to choose when emails within a folder will get automatically archived.
Here are some other ways to keep your mailbox size under control:
References: https://support.microsoft.com/en-us/office/manage-my-mailbox-size-792b521c-3f4e-404e-b436-9c197bad6f45 https://support.microsoft.com/en-us/office/organize-your-inbox-9aea8ad7-883d-459b-a3ea-ae20f06cfb32#ID0EBBBBF=Web