>POP3 protocol typically deletes the email upon retrieval

What POP3 client are you using that does this? I've not seen it before. It gets marked as read but that's it.

Geez, Eudora? Outlook Express maybe? I haven’t used POP3 in a decade.

It used to delete from the server after downloading locally. This was when most email mailboxes had a capacity of 10MB.

I'm writing something that uses POP3 right now and thankfully it doesn't delete anything. I'd have to do things a lot differently if that were the case

So you think google storage systems work like your normal filesystem?

You don’t think that files can be deleted from a Google file system? Does gmail even store email like that, in flat files?

They can be but not instantaneously, because of multiple replicated copies in a distributed environment.