I've been an Independent Software Vendor (ISV) for over 20 years now providing IT solutions for the IBM i community (known previously as the AS/400, iSeries, System i, etc).  
As with any product or solution, support is one of the biggest selling points, and to me, one of the most important offerings from an ISV.  That's why we always strive to give the absolute best support possible.  Especially nights, weekends and holidays (when most IT professionals are doing upgrades and enhancements).

But when does support for your product stop being support, and start to become support for the hardware, the OS, or even fall into the category of "education"?  
For example, a customer just installed new hardware and calls support because email isn't working.  The email client they are using is your software which they transferred from another machine.  
The support call ends up being a 2 hour crash course educating your customer or client on some basic topics such as how mail routers, DNS servers and  TCPIP work, and how to set them up properly.  Most likely these things were set up on the old hardware by someone else, and not set up on the new hardware.   
Is this type of support expected?  Should it be billable?  If so, do you just refuse to help if they don't want to be billed?  
The reason I pose this question is over the past 20 years I've personally dealt with thousands of customers all over the world.  Within that group there is also varying degrees of education and technical know-how.
On one end of the spectrum there are those that take a piece of software, download it, install it and get it working.  I rarely hear from them (except for enhancements requests, which we love to get!)
On the other end of the spectrum there are those that need assistance creating a job log, adding a library to a library list, importing SSL Certificate Authorities and everything in between.
There is a line where product support becomes "education" and probably should be a billable event.
I would be curious to hear from other successful ISVs who include support with the cost of their product on how you handle similar situations.
I also would be curious to hear what customers expect from ISVs in the same situation.