Please help me this case : my helpdesk system version 8.0

- When user send mail to support@abc.com , it auto create a ticket on system (good) and send mail notify to technician with email have ID ticket (example : ID 1234 ) on subject . But when technician reply email (re: ....ID 1234) , it not auto merge to old ticket (ID 1234) , it create new one (ID 1235).

Please help,

Thanks

Tom