Werk #11792: mail: adjustments to the number of graphs

This werk affects all users who use the mail (not asciimail) plugin. If your emails contain performance graphs only the first 5 graphs will be sent by default. Additionally, if you use notification bulking only graphs for the first 5 notifications in a bulk will be sent.

You can adjust these settings with the options "Graphs per notification" and "Bulk notifications with graphs" either directly in the notification rule or with the ruleset "Parameters for HTML Email".

Reason behind this werk: Each graph in a bulk increases the size of the mail and takes time to render on the monitoring server. For very large bulks the mail size may exceed the maximum size for attachements or the plugin may run into a timeout so that a failed notification is produced. This werk will therefore increase the liability and performance of HTML emails. Since most services have fewer than five graphs and the most important information is displayed in the first graphs a total number of 5 graphs should be sufficient even in single notifications. Furthermore, for a detailed analysis the data displayed in emails is usually not sufficient and a look into the user interface is necessary.

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