开源协议

http://dl2.iteye.com/upload/attachment/0047/4142/d770c85a-49b7-3c7f-8ae2-cbb6451e00d8.png

libcurl

http://www.codepool.biz/build-use-libcurl-vs2015-windows.html

测试 smtp service

https://www.smtper.net/

can i use?

https://caniuse.com