How do I get my iphone to show my yahoo and gmail messages as read after I read them on my desktop? If I read them on my phone, they show up as read on my desktop.
You want to make sure that the email is setup as (and supports) IMAP.
Note also, though, that even it is it set up correctly, there might be a delay between when they are shown as read on one device to when that gets refreshed on the other device.