Configure open source Help Desk

SDP Plus from Manage engine (free version) or OS Ticket or something similar to deliver following objectives:
Previous knowledge and experience of customization of such suggested software is a must.
1. Create an entry (call it an order or a ticket) in the system with an email (this is important feature and must have)
2. Amends the exiting ticket via email using some reference number in the subject line
3. Multiple groups to use the same system and have a dashboard to track the assigned or unassigned tickets
4. Each group may have one email or multiple emails to create/update the tickets
5. User logins and access to ticket depends on the group memberships (one user can have more than one group membership)
6. Some mechanism to notify users if
- A new ticket is created
- Tickets are not updated for certain period based on SLA defined
- Identify the tickets which failed to meet the SLAs and also identify the user who is assigned to such tickets
7. Multiple domain emails
8. Available on desktop and as a mobile app
9. Available to external user and customers