It depends upon the size of the individual email. In the early 2000's email attachments were less common and on average smaller in size. Today, 20 years later, it is common in my line of work to see email attachments in the 5-10MB range. Pass them back and forth a couple of dozen times for changes and approvals and it doesn't take long for it to balloon. Yesterday, I worked on an outlook email issue on a PST file that contained 40,000 emails and was over 10 GB in size. His PST was new less than two years ago.

It really depends upon how it is used, misused or abused.