transferring from iPhone to MacBook Air

For this, you really don't need to physically connect the two devices to see the same thing on both.

For email (assuming your email account(s) is/are IMAP) you'd only need to set them up in Apple Mail: Add email accounts in Mail on Mac - Apple Support. Once that's done, you'll see the same emails on both devices. Read an email on one device, it will automatically show as read on the other. Delete an email on one, and it's gone from the other.

By the way, you can do a similar thing with photos: Set up and use iCloud Photos - Apple Support. Take a photo with your phone, and it will be available on your Mac.

Hope this helps.

(And, BTW, there's no Migration Assistant from iPhone to Mac).