It started with me finding spotlight results from Mail when I searched for my notes. Apparently the content of hundreds of my notes are in my gmail account, according to Mail. I have not had notes sync enabled for that account for a long time.
I navigate back in Mail from the opened spotlight result, trying to determine which mailbox the email is in. Apparently it's in mailbox Xyz which is the name of a folder from the notes app, but that mailbox doesn't exist in Mail app nor in the Gmail app.
I delete the Gmail account entirely from my phone, but I can still search for, and open, these phantom emails.
I reboot the device — no difference.
I look closer: the emails are addressed from me, but not to anyone. They don't appear in my unified sent box, and I can't find any trace of "real" emails from the deleted account.
Where are these emails/notes located, how did they get there, how do I ensure that I'm rid of them all and how do I prevent this from occurring in the future?
I have many notes that I don't want to remain on some mail server long after I think I've deleted them.
Update Disabling mail sync for my iCloud account makes Mail unable to display the emails when opened from spotlight.
iPhone 5, iOS 10.3.1