It would have to be from an app if a notification. Do you mean email? If a notification you should be able to long press it and see which app is responsible.
I think I got it. I thought I had all the apps I didn't want notifications for blocked but I didn't have Chrome blocked. Now I do. I'll see if that works. Thank you.
Go to Settings, Apps and find Chrome. Do a force stop, then clear cache and clear data. Exit Settings and reboot the phone. May help. If not, consider an ad blocker for Chrome or, like I did, throw the sucker in the trash. Chrome, not the phone
Okay, you were typing while I was. Hope that does it, if not see above.