- Ensure email notifications are on for User A for a given topic, such that User A receives an email notification for every reply to that topic. (Or, every post in a category.)
- Have User B reply to the topic.
- Immediately after (1-2 minutes, or within the editing window established), have User C reply to the same topic.
- Email notification from User B arrives before the notification from User C.
- Email notification from User C may arrive before the notification from User B.