Email Command REQUESTERE-MAIL not working

I currently have the email command parsing working. I can specify many items including REQUESTTEMPLATE, PRIORITY, etc. But one that doesn't work, an important one, is REQUESTERE-MAIL.

My scenario is that I can creating a web page (the web server, email server, and SDP server are all internal, on-premises servers) that takes a request subject and request description and creates an email and sends it to SDP. I am going to create this email object (in C#) and specify the FROM as being a known requester. But I want to change the requester in the request to be the email address of the internal, company user using the web page.

Right now I cannot change the requester with the command REQUESTERE-MAIL. If I do:

@@REQUESTERE-MAIL= test@test.com@@

In the ticket, the requester email still comes up as mine (as I am sending the email right now).

Any ideas?