I agree with Elegran. Your email password has somehow been exposed. The email provider needs to investigate and must report data breaches to the Information Commissioner. Ask that the account be closed as well, you say that you don't use it.
If you use the same password elsewhere, change it straight away, use more complex passwords as simple ones are easily 'cracked'.
This sounds like a clumsy attempt to frighten you. Don't respond and block the sender.
Grandad1943, while I agree that Google OS is currently very secure, you have to ask if protection extends from the Chromebook to email recipients' devices and whether or not any third party servers are involved.
Mandelson's Global Consultancy Goes Bust...
advice please DGS requires speech therapy



