.Net版本必须在Web服务和网站之间匹配吗？

I have an existing website that is currently using .Net 3.5 and must stay that way because of our sharepoint integration. I need to write a web service/web api that the website will interact with (a method to send an email, for example). I also need to write a windows service that is going to do the same thing. The windows service will probably be .Net 4.5.I have an existing website that is currently us