Compiling a .java from another plugin

Been looking for a mail plugin that isn't more work than it should be but have only found essentials and postoffice(more work than it should be). Thankfully Essentials is opensource so I was able to find the mail portion of it(Commandmail.java) Source File

How would I compile this so I'd only have the mail portion of the plugin? I'm open to using other plugins but I don't feel like jumping through the hoops I felt I was jumping through for postoffice.

Oh should definently mention... I'm very inexperienced with java right now, still learning it in school(so very slowly...)