Ticketing design

[s2b-git]

If we talking about converting emails to tickets I believe Ticket should be referenced 1:1 to

1. Contact only (if contact is not linked to any account). Here mailconverter should automatically create new contact
2. Account only (if converted email address is found in Account but not in Contacts)
3. Contact and Account to which Contact belongs to

This would follow banking scheme:
Corporate Account - multiple users access (contacts)
Private account - single user

Here we need to remember that ticket is always "personal" as in ticket case we dont deal with bots but with certain individuals.
This can be reflected in customer portal where contact will see all own tickets, or all tickets assigned to Account to which contact is linked (depending on access rights design).

Ref: #11947