If you use Outlook on a windows PC you can export a folder of emails to a spreadsheet. So, for instance, if you have correspondence that you want to keep but don’t need to refer to much, you can export to a spreadsheet and delete the files from Outlook.
If you are running Outlook on a Mac, you don’t have that option – the only thing you can do is export all your emails to a file.
On a Mac, the best, and easiest thing to do is:
Create a new folder (on the desktop, or wherever you like)
Drag and drop emails from Outlook to the folder (you can do this one at a time, or you can select multiple messages), then delete the emails from Outlook.
When you look at the emails saved in the folder, they will have lost some of their formatting, but all the important information is intact, so you have a record of the correspondence.
By the way – this will also work on Windows.