Change "You have new messages in your conversation" subject line

It isn't exactly straightforward, especially for customers who emailed in and didn't use the chat box to contact us. Please either keep the subject line they used to contact us or let us set the subject line for all messages. We've noticed more customers saying we never got back to them because they saw that odd subject line and knew it wasn't the one they used to write us. Even Gmail won't see it as a reply to their email and it will show as a brand new message.