I use POP3 for some services. I have one mailbox that I share with my wife as a joint household e-mail address (we both also have personal addresses). Having syncing between devices would be a nightmare as things would get marked read by the other person. Yes, I could set it up to forward to our personal mailboxes, but it's been working fine for 20 years, so why change.
More importantly with POP - you mail gets downloaded to your device and then that's it. It's yours, secure, for you to manage. With IMAP there's always the possibility of the ISPs server hiccuping and deleting mail off your machine that you thought you had safely downloaded.
Even with IMAP, you can secure messages by moving them to local folders. And with multiple devices, you can move a different set of messages to each device. You can also move messages back to the inbox, in order to share with another device.
I used to be a POP fanatic, mostly because I didn't like the idea of leaving copies on the server. But then, the NSA probably logs everything, so hey.
You can run POP3 without deleting mail from the server. The POP3 commands for "download message" and "delete message" are completely independent; I typically have my mail client set to delete messages from the server 14 days after downloading them, so that I'll always have recent email in two places.
I know people that use it because they think it is better from a privacy standpoint.
It might not be correct now but at one point the Electronic Communications Privacy Act stipulated that data left on a server for more than 180 days is considered to be abandoned and the government can easily and legally access it.
Yes, there is that. But in reality, the NSA arguably has copies of everything. Or at least, metadata. And it almost certainly retains copies of all encrypted messages.
I'm more worried about the situation where somebody reveals some corruption in a small town police department and the police decide to investigate that individual by looking at that person's "abandoned" data.
