In response to Mailbox Cleanup by Diana Huggins, Gnomie Ron Davis writes:

An important tool in managing e-mail messages is a rich directory structure in
your personal folders. I can’t get very specific, because the right structure
will be different for each person, but the top level, for example, might be a
folder for each of “Friends,” “Businesses,” “Family,” “Government,”
“Subscriptions,” and the like. The next level in each folder might be a folder
for various groups. For example, under “Businesses,” there might be a folder
for each type of business, such as “Computers,” “Books,” etc.

This organization works well for me, and has impressed bosses both in the
explanation and in the result - sometimes finding a relevant message from
years ago in seconds. I think your readers would benefit greatly from it.