KevinTheJedi
This happened to me again yesterday so I dug a little more into it. What happened was the customer went to their Sent folder in their email and found a ticket they generated in the past. In Outlook, they took that same email changed the subject line and changed the body to reflect the current problem. Because it was from the same thread it did not generate a new ticket and the system did not see it as a message, hence, no email alert at all.
I replicated this on two different tickets