Pairing between iPhone and iPad

That would have nothing to do with Bluetooth, at all.

The syncing for your email happens at your email provider's servers. Each device accessing the same email account would get the same email as long as its set to IMAP.

As long as the email account type is IMAP emails should sync. If the email account is POP3 they will not sync.

Check Settings->Mail->Accounts and make sure everything is correct. You may want to turn off the mail switch on both devices, and then turn it on again.

What, specifically, are you attempting to achieve by pairing an iPhone and iPad over a Bluetooth connection?

Whilst it is technically possible to do so, for the majority of applications, Bluetooth pairing of an iPad and iPhone is entirely pointless. If your intention is to use Cellular Hotspot features of your iPhone, this link is optimally achieved using the native WiFi hotspot connection - this being a largely automated process. Hotspot connections over WiFi offer substantially greater throughput, range and reliability.

How to set up a Personal Hotspot on your iPhone or iPad – Apple Support

If you still wish to pair your iPad and iPhone over Bluetooth, you first need to manually enable the hotspot feature on your iPhone:

Settings > Mobile Data > Personal Hotspot > Allow Others to Join - set to ON

Next, Bluetooth for both the iPad and iPhone must be placed in Discovery mode:

Settings > Bluetooth (accessing this page will automatically place the device in Discovery mode)

Whilst both iPad and iPhone are in Discovery mode, you can mutually pair the devices.

Again, I must stress, unless you have an unusual “edge case”, pairing of iPad and iPhone over Bluetooth offers no technical benefit.

Phil - whilst not widely know or publicised, this feature has been accessible (although with some difficulty) for a very long time. The iPhone hotspot can be accessed via WiFi, BT and direct cable connection over the Lightning connection.

As outlined, unless very specific edge cases preclude use of the WiFi Hotspot, hotspot pairing/access via bluetooth offers no benefit.

How to set up a Personal Hotspot on your iPhone or iPad - Apple Support

No, it wasn't. Apple devices have never been able to pair directly over bluetooth except when using Personal Hotspot.

While Bluetooth is used for other features between iPhone and iPad none of them require direct paring. What exactly are you trying to accomplish by paring them?

Yeah, that's what I said. 😉😜 There is no direct pairing except when using Personal Hotspot. Meaning it works for Personal Hotspot.

Apple devices have never been able to pair directly over bluetooth except when using Personal Hotspot.

Email is not synced directly between the devices. It's synced through the email servers.

Again: Who is your email provider? Are you logged into the email account on both devices? Is it a POP email account? Or IMAP?

I have an iPhone, Mac, Watch and iPad. iOS 15.2.1 has had no effect on my email.

Who is your email provider? Are you logged into the email account on both devices? Is it a POP email account? Or IMAP?

Add an email account to your iPhone, iPad, or iPod touch - Apple Support

I seem to have misread you initial reply - for which I must apologise. We’re clearly in complete agreement 😊

It’s been a busy day… 🚒🚑

No worries. It happens. 🤗