Don't open them, you should forward them to the banks fraud department, at least that's what I was tools to do as my bank told me they'd never try to contact me by email.
(I hope you are well)
I've had messages from banks I haven't used, when I can I forward them to the appropriate place - you could pop into one of their branches and ask for an email address for the fraud department, or simply just delete them! Chance are they are scammers anyway and ought not to be encouraged! Besides I have a suspicious nature anyway - put it down to having worked in banking
There's a message on the Santander online banking site advising the there is mass scamming going on. If you receive anything purportedly from Santander you can forward it to [email protected]
Millions of these fishing emails are sent out every day, so all the major Banks have more than enough info to proceed with their investigations. So I can't see the point in letting them know about any more. Just delete them, and never, ever reply to them !