Using a mailslot on the client is incredibly easy. You can use the STREAM built-in function to open it, just like a regular file. But you must use the 'OPEN WRITE SHARE' mode. Here then is how we would open the "blort" mailslot on a computer named "MyComputer":
/* Open the blort mailslot on MyComputer */
mailslotname = "\\MyComputer\mailslot\blort"
IF STREAM(mailslotname, 'C', 'OPEN WRITE SHARED') \== "READY:" THEN
   SAY "ERROR getting mailslot:" STREAM(mailslotname, 'D')