How to synch Mail across my Apple devices
I use a iPhone 12 and ipad11 pro with iOS 17.1 and a MacBook Pro with iOS 12.1
iPhone 12 Pro, iOS 17
Ordinarily, this is automatic - it just happens.
The fact you’re asking, though, indicates that something isn’t working that way for you - that is, assuming you’v tried setting it up and it isn’t working - if you haven’t yet started for fear of doing it wrong, just go ahead - you might be pleasantly surprised :)
If you have setup multiple devices and it’s not working then you’re going to need to provide more information, though, as to your setup, specifically some details about the email accounts you’re using - if you’re using an iCloud account, for example, it should just work. The same for Microsoft Exchange, and Google GMail accounts.
Most other accounts that use IMAP as the mail standard should also work - IMAP is designed to use server-side information to sync across multiple devices.
If you’re using an older account that uses POP, then you have a whole different scenario (and world of pain), since POP was never designed to support multiple accesses.
Without knowing the server setup for your account, it isn’t possible to determine what might not be working for you.