diff --git a/collects/net/smtp-sig.ss b/collects/net/smtp-sig.ss
index 004d81d..96dd7c7 100644
--- a/collects/net/smtp-sig.ss
+++ b/collects/net/smtp-sig.ss
@@ -4,7 +4,8 @@
 
   (provide net:smtp^)
   (define-signature net:smtp^
-    (smtp-send-message
+    (smtp-sending-server
+     smtp-send-message
      smtp-send-message*
      smtp-sending-end-of-message)))
 
diff --git a/collects/net/smtp-unit.ss b/collects/net/smtp-unit.ss
index 5b34a5d..fb95ca3 100644
--- a/collects/net/smtp-unit.ss
+++ b/collects/net/smtp-unit.ss
@@ -11,7 +11,7 @@
     (unit/sig net:smtp^
       (import)
 
-      (define ID "localhost")
+      (define smtp-sending-server (make-parameter "localhost"))
 
       (define debug-via-stdio? #f)
 
@@ -70,7 +70,7 @@
 				    (raise x))])
 	      (check-reply r 220 w)
 	      (log "hello~n")
-	      (fprintf w "EHLO ~a~a" ID crlf)
+	      (fprintf w "EHLO ~a~a" (smtp-sending-server) crlf)
 	      (check-reply r 250 w)
 	      
 	      (when auth-user