I meant create a "meta" data source, create a point in it, and give it any old script to give the point a value.
I've personally had some issues with Ubuntu, but i'm far from being able to say for sure that's the problem. Still, i suggest trying Fedora or a Windows host for Mango to see if your serial ports stick around longer.
Also, make sure data sources and testers aren't competing for the port in the case that you have multiple data sources running. Only one running data source can own a serial port at a time. Note also that the node scanner owns the port while it is scanning.
The message could come from multiple places, but in general it means that the TCP connection to your modbus equipment was closed, and not by Mango. When you are using the keep-alive, Mango detects the condition and attempts a re-connect upon the next polling. If the stream was closed during a poll, the remainder of the poll will fail. Overall it indicates network problems.
It's a two step process (assuming you have Mango already pulling data from your sensor). Edit the point by adding a point event detector (either a high limit, a low limit, or both in your case), and save. Then, head over to the event handlers page and add an email handlers to your event(s). That's it.
The division between events and handlers allows 1) events to generated in arbitrary ways, and 2) events to be handled in multiple ways.