Multiple versions of single email in Trash

I suggest the following workaround. Open Mail's preferences and go to Accounts. Then select the offending account on the left and choose "mailbox behaviors" on the right. Uncheck the box by Drafts: Store draft messages on the server. Of course, your draft messages won't sync between devices anymore, but it will definitely fix the problem.

Matthew – I use this workaround for my GMail account and it's really helpful - MOST of those drafts do not show up there, but some still do. It used to be that I'd get like 20 versions of each email I typed. Now, occasionally, I get an email I sent showing up in my drafts folder and I have to wonder if it actually sent or did not. I'm still hoping there's a way to make those stop, too, unless I intentionally save a draft, but it sounds like that might just be a shortcoming of the relationship between GMail and Apple Mail...? :-0

The file WK resources gets created and are moved to trash see an article macOS Sierra: If the Trash contains folders of recovered files

However, Apple Mail also saves incomplete versions of emails in 'Drafts', even though I don't save them to Drafts and even after I send them. This happens to emails from other services too, not just AOL.

That's correct. For example I noticed that certain Microsoft Exchange servers will save multiple copies of mail messages in its Drafts folder as they are being composed.

Apple should be working out these kinks with the services for us. I'm guessing this doesn't happen with AOL and MS Outlook.

Apple's Mail app conforms to industry standards that others choose to ignore. AOL's email services might not conform; I don't know. I do know that Microsoft routinely chooses to ignore them, believing the entire world uses Outlook.

I have this same problem, although it only happens on my Mac, not on my iPad or iPhone... suggests? there should be a setting somewhere on the Mac? ... when I uncheck the box 'store draft messages on the server' it simply rechecks itself...

That action is being performed by your email service provider.

I understand. Unfortunately I don't believe that behavior is anything you can control. MS Exchange's habit of saving multiple copies to Drafts (at least once every minute) did not correct itself until the company with which I corresponded updated their Exchange server to whatever they're using now. I didn't change anything. I'm just assuming AOL is doing something similar.

Any last advice?

Maybe try rebuilding the Mail database by following these instructions: Mail for Mac: Rebuild mailboxes. It's harmless, but I'd be remiss if I didn't recommend creating a Time Machine or equivalent backup first. If rebuilding the Mail database causes a message to become lost, it was probably corrupted to begin with.

I hate calling AOL!

Don't bother. They are nearly certain to blame Apple, or you... anyone but themselves, and their customer-level support probably hasn't the slightest clue as to how their email servers work. It will just be an exercise in frustration.