POP or IMAP My husband and I both use our one company email address to view and access emails from different devices.

We have a current situation where if I view an email from my iPhone, and then delete it, I lose access to it from my MacBook. Or if I view it from a device, my husband cannot view that same email from his iPhone. Is this to do with the POP or IMAP setting on our devices? What is the best way for us to be able to view and then save or delete emails from various devices yet still have them available to view etc from another device? This used to work okay for us, but recently we have been unable to view emails that the other has opened.