Support Email Address limitations

Support Email Address limitations

I am having issues with the limitations of the Support Email Address.
The docs describe that you can have unlimited From Addresses but only 100 Support Email address (Enterprise).
However, this does not make sense.

Scenario:
xyz@mycompany.zohodesk.com linked to Dept1
From Address: xyz@mycompany.com linked to Dept1
So now I setup a Forward in my Mail that forwards xyz@mycompany.com to xyz@mycompany.zohodesk.com

This is, of course, working as expected.

Now I create another From Address: abc@mycompany.com
Forward in my Mail to support@mycompany.zohodesk.com as there is no associated @mycompany.zohodesk.com address configured, but there is a abc@mycompany.com From address.


Flow:
I receive an email on abc@mycompany.com, this is moved into Desk through general suppport department.
I move the ticket through my Dept1 department in Desk.

I reply to this ticket, but and choose abc@mycompany.com as Reply.
Our client gets the reply on this address, and makes a reply himself.
The mail abc@mycompany.com is forwarded to support@mycompany.zohodesk.com as always.
This original mails contains the [## 123 ##] in the subject.

What happens is that there is now a NEW ticket in the general department, although the underlying ticket number itself is still 123. Also because of the new ticket, the reply is not added to the thread of the original one.


So the only way to fix this, is to have 1-on-1 Support Mail and Reply Mail, but then there can only be 100 of them.
As we will go beyond that limit, I tried already different things but keep hitting these issues.
I tried to create tickets through API instead of forwarding, but then I have no way to set the initial To mail so that an agent will get the original To mail. I can create the ticket through API but I cannot create the underlying Thread to simulate the mail thread with all the information like content, attachment, from, to, etc.

I really need help on this, otherwise I think I need to move to another platform where there is no limitation on the number of mails.

Can anybody help?