Initialize send_status at the function's start

lib/msf/core/exploit/smtp_deliver.rb

@@ -127,6 +127,7 @@ module Exploit::Remote::SMTPDeliver
   # not already established.
   #
   def send_message(data)
+    send_status = nil
 
     already_connected = connected?
     if already_connected
@@ -143,7 +144,6 @@ module Exploit::Remote::SMTPDeliver
 
     # Avoid sending tons of data and killing the connection if the server
     # didn't like us.
-    send_status = nil
     if not resp or not resp[0,3] == '354'
       print_error("Server refused our mail")
     else