Based on an option we had in a different system - we could generate an email address that's specific to a particular ticket, so when we send an email with this address in BCC, the message also pops up in that ticket.

The issue is that Zoho doesn't support duplicating messages nor tickets (the so called "duplicate ticket" definitely does not duplicate a ticket but just creates a new empty one with some prefilled info), so currently there's no easy way to include a message in several tickets. This idea could help with this.