With Evolution MAPI providers, you can view the size of a selected folder.
You can view the folder size by using the following methods:
Select Edit > Preferences > MAPI Account > Edit.
Select the Exchange settings tab.
Select Folder size.

Alternatively, right-click the MAPI Account in the folder tree, then select folder size.

A Folder dialog is displayed with details, such as folder name and their respective size. It also provides you the total mailbox size.