Is there any way to have RT use some kind of "reply above this line" email delimiter?

[GreenJimll]

@Alex_Hall

Exactly. The templates would include

– Reply above this line –

at the top, after which are all the transaction details. New ticket, owner change, reply, comment, it doesn’t matter. Every template would have that line at the top. When an email came in, if that line were found in it, everything above the line would be processed by RT, while everything below it would be discarded. If the line were absent, the entire email would be processed, as that’s likely a new ticket being sent in via email.

Remember to tell people who do inline quoting in their reply that they’ll need to remove that line, otherwise you’ll potentially lose all/part of the reply they were sending in.