Tickets do not “magically” switch groups upon follow ups, unless you told a filter or trigger to do so.
Please provide the tickets history as I’m sure the normal fetch process doesn’t do this.
Well ok, the group didn’t change, but the the wrong group was assigned.
Email A goes to Group A, Email B to Group B
When mailing from Group A to Email B, the newly created ticket in Group A is updated. I would expect a new ticket in Group B, because the mail was send to Email B and Email B has nothing to do with Group A.
That’s the reason why Zammad updates the ticket on Group A.
If you reply or forward a mail to a Zammad owned alias, it will recognize it’s ticket number as a follow up and thus update the original ticket.
What you’re looking for is ticket splitting and then moving it to another group.
Personally I don’t think it makes any sense to send a mail from group A that then leaves Zammad via MTA, makes some journey over your MTAs, gets into an inbox and gets fetched by Zammad to group B (where it recognizes the follow up and thus updates the original ticket).