apparently e-mail is not much reliable for storing/keeping files. there have been cases where an old email with an attachment would not load correctly because the servers just erased the attachment file.
This was a custom email server though, there never were any emails, it just presented files as though they were so that a client would download them.
Actually caused some problems for email clients, as they usually assumed emails were small. I got a few of them to crash with 200 Mb "attachments" (although this was in the early 00s, 200Mb was bigger than it is today).
Since GP says it was a POP3 server, I suppose you would set up an email account in your client with its inbox server pointing to that POP3 server. When the client requests the content of the inbox, the server responds with a list of "emails" that are really just files with some email header slapped on; so your email client's inbox window essentially becomes a file browser.
