Which is the easiest way to sync email across two macs, an iphone and ipad, so that I can delete a mail on one device/computer and it automatically gets deleted on the other devices? is that possible at all?
POP3 is going to be nothing be a giant hassle to try and sync. You need to find an email provider that uses IMAP. Free GMail can be configured to use IMAP. Maybe if you are locked in to the current POP3 account you could have it forwarded to GMail and use GMail IMAP.