If the "mail checker" icon on the panel is used, but no command is specified, the icon still "pressable" - it would be nice if the icon would not be "pressable" if no command was entered. Reproducible: Always Steps to Reproduce: 1. 2. 3.
Making the button insensitive also prevents the use of the right-click menu , so I don't think that is possible. If I don't think of some clever way to do this, I will probably close this report. Setting the severity to enhancement.
Ok, setting this to WONTFIX. Work is underway for a new mailwatch plugin.