If the email is sent from any Incident record using quick message functionality ( email client), the email is being sent successfully but the ticket "updated" date is not changing to current date on the source incident record
Few customers need the updated attribute to be set to current value in order to use them in reporting to fetch records on which the action was not taken in last few days.
Release or Environment
The email sent is an insert on the sys email table and has nothing to do with the current record from which the email is sent. You can only view the sent email on the activity log on the current record which is incident table from this KB perspective and it doesn't mean this is an update on the current incident record.
Platform is functioning as designed. If you still want to perform something , customisation is the ONLY option. As the quick message functionality is achieved by using send button on the email client, you need to try looking ways to customise this button or UI scripts followed by your custom business rules. Support will not be able to help much in this case as the platform is working as designed.