So now what, you have mailbox space of 100Gb so no more mailbox cleanup messages! But sometimes too much is too good, how best to organize? Here are some tips from Microsoft
This is a helpful one:
Conversation Clean Up is most useful on Conversations with many responses back and forth, especially with many recipients.
On the Home tab, in the Delete group, click Clean Up.
Click one of the following:
Clean Up Conversation The current Conversation is reviewed, and redundant messages are deleted.
Clean Up Folder All Conversations in the selected folder are reviewed, and redundant messages are deleted.
Clean Up Folder & Subfolders All Conversations in the selected folder and any folder that it contains are reviewed, and redundant messages are deleted.