Emails, which are automated should include an Auto-submitted header. Mail servers are then required to NOT send automated responses in response to these emails.

http://tools.ietf.org/html/rfc3834

• Automatic responses SHOULD NOT be issued in response to any
  message which contains an Auto-Submitted header field (see below),
  where that field has any value other than "no".

The proposed patch INCLUDES the 'Auto-Submitted' on all outbound emails created by the plugin. This header is defined as follows:

5. The Auto-Submitted header field

The purpose of the Auto-Submitted header field is to indicate that
the message was originated by an automatic process, or an automatic
responder, rather than by a human; and to facilitate automatic
filtering of messages from signal paths for which automatically
generated messages and automatic responses are not desirable.

...
The auto-generated keyword:

• SHOULD be used on messages generated by automatic (often periodic)
  processes (such as UNIX "cron jobs") which are not direct
  responses to other messages,

The Jenkins mailer-plugin creates emails by an automatic process and therefore SHOULD contain this header.