Thank you for your quick reply.
I checked that window and found that Mail, Maps and Safari were all checked. I have unchecked them and assume that that has solved my issue since the message from Siri has disappeared from the email.
However, I have the Enable Ask Siri box not checked on the Siri window. Shouldn't that turn Siri off completely? That's how it works for other Preferences in my experience. It appears to me that the Siri Suggestions... is not a subset of Ask Siri and perhaps it should be combined with the Siri window, with two sections, similar to the Security & Privacy/General window. I would see that as simpler and consistent with how other preferences work.