[plt-scheme] send-mail-message

Hi,

I am new to Scheme and am trying to send an email as follows:

 (send-mail-message "test at test.com"
                        "message-subject"
                        ( "test at test.com" )
                        '()
                        '()
                        ("test"))


I am getting the following compiler error:
"unbound identifier in module in: send-mail-message"

Could anyone please tell me what I'm doing wrong?

Thanks in advance.