class Net::SMTP

def debug_output=(arg)


end
....
smtp.start do |smtp|
smtp.set_debug_output $stderr
smtp = Net::SMTP.new(addr, port)
# example

You must call this before #start.
Set an output stream for debug logging.

Use this method for only debugging.
WARNING: This method causes serious security holes.
def debug_output=(arg)
  @debug_output = arg
end