Random rogue iphone emails coming back despite being deleted

Hi All,
I have this weird phenomenon in Apple Mail where a couple of emails keep coming back like bad pennies, despite deleting them in multiple ways (including banishing to “black hole” in SaneBox. They only appear on my iPhone XR (running 13.1.3) and connected Apple Watch, not on my laptop (running Mojave 10.14.6.or iPad (running 12.4.1). FWIW, both of them are group mailings, and both come in through my work account, which is Exchange. Any ideas about what’s going on or even who I should approach first?

I’ve had the issue a lot. Unfortunately, the only fix seems to be to remove the account from the affected device, and then to re-add the account.