- Select the Folder in the Folder view
- Select More message options (ellipsis icon) top right of the List view of messages in the selected Folder
- In the drop down menu:
Select Sort by Size
Select Ascending Sort order
That will show you messages in increasing size in the List view. As the Sort by size doesn't operate in reverse i.e. Big to Small you'd need to scroll down to the larger messages. I hope your mailbox doesn't contain too many messages!
