More alert for message not sent
When a message is not sent, there is just a small red x underneath the message.
It would be helpful to have a notification, make the menu item for that conversation red, or something else that notifies the user the message was not sent more explicitly. Not having the message sent and not knowing about it could cause trouble for some people.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information