+
+;;;###autoload
+(defvar smtp-open-connection-function #'open-network-stream
+ "*Function used for connecting to a SMTP server.
+The function will be called with the same four arguments as
+`open-network-stream' and should return a process object.
+Here is an example:
+
+\(setq smtp-open-connection-function
+ #'(lambda (name buffer host service)
+ (let ((process-connection-type nil))
+ (start-process name buffer \"ssh\" \"-C\" host
+ \"nc\" host service))))
+
+It connects to a SMTP server using \"ssh\" before actually connecting
+to the SMTP port. Where the command \"nc\" is the netcat executable;
+see http://www.atstake.com/research/tools/index.html#network_utilities
+for details. In addition, you will have to modify the value for
+`smtp-end-of-line' to \"\\n\" if you use \"telnet\" instead of \"nc\".")