Alert Mail (Graphs type change)

Hi,
I would like to know if I can attach the device_availability graph in the mail alert.

When the mail is delivered (correctly, no problems on this), the image at the bottom links to a specific URL:

https://xx.xx.xx/graph.php?type=device_ping&device=41

but I've got this error, and no graph is shown. 

Is it possibile to modify the configuration to insert the device_availability graph in the mail alert, instead?

https://xx.xx.xx/graph.php?type=device_availability&device=41

Thank you.