Why are SOCK5 proxies so hard to get?

I'm going to send out my mail using Atomic Mail Sender, but am having an extremely hard time getting my paws on some SOCK5 proxies-this is what AMS support said that the software required. I have reached a block, and need some insight as to why these specific type of proxies are needed. Why do they make it this way? Why can't I use regular private proxies that you purchase here in BHW marketplace? Should I use a different type of software for sending out my webmail that does not require SOCK5? Please help.