One way in which Nagios' notification system can be expanded is to create template-based e-mails. These will send notifications as both plain text and HTML messages. The template of the e-mail will be kept in separate files.
We will use Tcl for this purpose as it contains libraries for MIME (http://tcllib.sourceforge.net/doc/mime.html) and SMTP (http://tcllib.sourceforge.net/doc/smtp.html) functionality. The first one allows the creation of structured e-mails, whereas the latter one is used to send these using an SMTP server.
E-mails that contain content in multiple formats need to be wrapped in the
multipart/alternative MIME type. This type will contain two subparts: first the plain text version and then the HTML version. This order makes e-mail clients choose HTML over plain text if both the...