new iphone marking all email as read

[#1]

Help!
My new iphone is marking all incoming emails as read, so isn't notifying me when it comes in.
Any ideas?

[#2]

It appears that, unlike my old android phone, Plusnet's mail is marked as "read" if it downloads to my laptop first (even if I haven't read it). And my iphone is therefore taking that setting, and assuming it's been read.
I think!

[#3]

No, not that, I turned Outlook off, but it still downloaded the next email as "read". The only time it didn't was when I moved an unread mail out of the Junk folder on webmail.

[#4]

If you're using IMAP and you look at/open the email using any other program (Webmail included), then the IMAP seen flag will be set and the message will be marked as read across all other devices.