Hi - can anyone one answer (or direct me back to a previous thread) covering the issue of a mailbox keep re-downloading read emails whenever I turn off and switch back on my mobile? It's an Iphone 5S on ios 10, with a PlusNet email account. I end up with 500 emails re-downloaded again all marked as 'unread' when this happens.....! The phone is new to me so has been brought into use with an ICloud backup restore - some of the mail settings presumably need adjusting......... Thanks.
PlusNet Email system is primarily a web-mail system to be accessed via a browser, though it is possible to access through a mail client as well.
Looking at the questions in the Email forum it seems that all is not well in the land of PlusNet Email, and I suspect that the issue you are seeing is a result of that rather than anything to do with you mobile phone or your PN Mobile account.
On the top of the Email forum there are a couple of links on how to connect various email clients and there is a link through to Apple for iPhones. That may help you to confirm that your settings are correct on your phone. IF you get the chance you are looking at the IMAP settings for your iPhone mail client - not POP.