Email Command Fails to Update

So I have been trying to get email commands to work to update custom field in a ticket that would be a reply from a vendor with the tracking# for a part order. But it does not work

Subject: Requester 955 [RequestID: ##407##] @@SDP@@

Now I have tried numerous differences in the body field but it simply just adds it as a conversation to the ticket and never updates the field in question. Examples below on what I have used.
------
@@OPERATION=EDIT_REQUEST@@
@@WORKORDERID=407@@
@@UDF_LONG1=1234@@
-----
@@OPERATION=EDIT_REQUEST@@
@@UDF_LONG1=1234@@
-----
@@OPERATION=EDIT_REQUEST@@
@@WORKORDERID=407@@
@@Tracking=1234@@
------
@@OPERATION= EDIT_REQUEST@@
@@WORKORDERID= 407@@
@@UDF_LONG1= 1234@@

None of this seems to work, I even have a support ticket with the support team and they still could not figure out why its not working. I have also tried all above formats in plain text instead of html and it doesn't change anything.