Clojure's container structure

Here is some quick and dirty graph of clojure's container structure:

smtp.web.de fails to send emails

Recently a friend of mine, who uses my mail service, complained about e-mail not being received from users of WEB.DE. The sender received an error mail with following content:

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of
its recipients. This is a permanent error. The following address
failed:

  <nix@example.com>

domain name system error:
domain has no mail exchangers

Rotkäppchen

Es war ein mal ein kleines, süßes Mädchen, das immer ein Käppchen aus roten Samt trug. Aufgrund dieses Attributes erhielt es ein Assign unter dem symbolischen Namen Rotkäppchen.