In the case of eaze, marijuana is not legal federally so you can’t use traditional postage or banks that cross state lines.
In some places you can get alcohol delivered, and others, you cannot. I'm sure that as time goes on, and with federal legalization, restrictions will ease on shipping cannabis.
One thing to note is that the black market uses mail to transport cannabis in a major way… Not just the darknet vendors, but many other people. They even make rap songs about it. Home delivery of cannabis has long been popular in dense urban markets such as New York City and San Francisco, also.