Zoho Desk - E-mail Subjects / Ticket Guessing / Hijacking

Zoho Desk - E-mail Subjects / Ticket Guessing / Hijacking

We have an existing ticket system that uses numeric ticket IDs, and also in the e-mails [!50822]

To avoid conflicts, our starting Ticket ID in Zoho Desk is #60000

Where can I find more information about the behaviour and controls relating to Ticket IDs and e-mail parsing:
  1. Are the Ticket IDs unique across Zoho Desk, or unique within a department?
  2. Does Zoho Desk use Regex to parse the subject? ##60000## or #60000 or !60000 - what is the standard pattern?

1) 
Ticket #60000 has Bob@domain.null as a Contact
E-mails are sent to Bob@domain.null with subject #60000
Kevin@otherdomain.null e-mails Zoho Desk with #60000 in the subject
Is a new ticket created?

2) 
Ticket #60000 has Bob@domain.null as a Contact
E-mails are sent to Bob@domain.null with subject #60000
Someone replies with a subject of #60000 !51222
Is a new ticket created or added to #60000

3) 
Ticket #60000 has Bob@domain.null as a Contact
E-mails are sent to Bob@domain.null with subject #60000
Someone replies with a subject of #60000 #51222
Is a new ticket created or added to #60000

Thanks