"This ticket is closed and merged into ticket xxxxx"

Would it also be possible to edit this message with the other email notification templates?

I would like the ability to turn this email off -- once the customers are creating duplicates and getting confused, this email just serves to confuse them further.

These emails are of no use.  As the customer does not usually know the whole email trail when they receive the message seeing a message saying something like "this ticket is closed and has been merged with ticket number 1234" just leads to make further enquiries about ticket 1234 which they may not be aware of.

This can be stopped by marking the message as private when the ticket is closed.  However, this should be configurable and be able to be switched off permanntly.  In the absence of a permanent switch it should be possible to customize the email message that goes to the customer so they can at least be informed of what the ticket relates to.

I do also agree that this notification towards the customer has little or no use at all. At agent's side, this is anyhow useful, but a link to another ticket would be excellent.

I would also make the merge information visible more clearly in the original ticket, and also forward possible replies to the original ticket to the new ticket.