POP settings still deleting email from server
My home network includes a desktop PC (Windows 10), laptop (Windows 10), and my iPhone 6. I use Thunderbird on both the desktop and laptop, and both are set to leave email on the servers for all my email accounts, which are POP. When I view email first on the desktop or laptop and erase it there, email still appears on my iPhone, as I want it to. But when an email arrives and I view it first on my iPhone, if I erase it from the iPhone, it doesn't appear on the laptop or the desktop PC. What setting am I missing on the iPhone so that the iPhone doesn't remove emails from their servers?
I deleted my gmail account and then re-created it. I had to trick the iPhone into letting me customize the settings--I entered a gibberish email address and name, and when it couldn't verify them, the iPhone let me enter my own settings. I established the account again with POP settings. I've confirmed in the incoming settings that "Delete from server" is set to never, but the iPhone is still deleting messages from the server. As before, when I delete a message from the iPhone, it doesn't appear on my laptop or desktop PC. Any idea why and how to correct this problem? Thanks.