It's not a question that has ever come up before - I guess most people only send the camera email alerts to themselves and therefore don't worry about it.
We are often told that you must not send confidential information by e-mail. Isn't the S/N a piece of information that can make it easier for hackers?
My camera emails normally go to myself, yes, but alarms also go to the alarm company and possibly my electrician who assists in the event of a fault. None of these need a serial number and neither do I.
We have spoken to Hikvision support and they have confirmed that there is no way to remove to serial number from the email notifications.
In our experience, the security risk is very low if people see your device serial numbers because they would still need your device password and/or Hik-connect Encryption Key to gain any kind of access to your cameras. Keep your passwords strong and your cameras will remain secure.