Actually, Microsoft has end-of-life'd WLM and it no longer works properly on W10. It appears to, but it won't work on many ISP-provided webmails such as Cox, Charter, Verizon, AT&T Uverse, Comcast, etc. WLM was replaced by the W10 native Mail app, which will work with your imported WLM message store via the import function. However, there are still multiple issues with using ISP-provided webmail apps, and I have written an entire post about how to get around that. (you can search this forum for "WLM" and find it). Microsoft no longer supports the updates for WLM and you can continue to use it as Norway suggests, however it's going to be full of security holes just like XP now that MS no longer supports that product either!
The real issue is the lack of functionality, if you use your E-mail for business, or school, and personal or all 3. The removed many features such as the ability to get Mail delivery receipts, and several other functions such as Group lists. Your only solution is to get off WLM and go to direct free webmail such as Yahoo, Gmail, AOL, or Outlook.com or purchase the full Outlook app that comes with either Office365 subscription (which I now run on all my PCs) which includes the Full version of Outlook 2016 or you can buy the standalone MS Office 2016 Desktop which comes with the same app, Outlook 2016 which includes the built-in Mail Client. This is the direction I went. I couldn't use Outlook since Outlook 2010 came out, due to the cost of the product. I used WLM on all my PCs for 5 years, as it was free as you know. But, now that it's gone and I can afford it, I'm back to using Outlook which is a full-featured E-mail program and I have used it since 1997.
There is another alternative between Outlook and WLM i.e. EM Mail which is a nice little program free for up to 2 email addresses and paid after that, that has a lot of nice features and is not "Spartan" like Windows 10 Mail. eM Client