Windows Live Mail 2012 works fine with Windows 10 as long as you DO NOT install the update KB3093594.
This only applies as long any Microsoft Email account you're using has not been upgraded to Outlook Mail. When that happens, you will no longer be able to synchronize the account's mail folders using DeltaSync, and you won't be able to synchronize contacts and calendar with this account, either.
This is what I mean. When the Microsoft mail is altered and fails to Sync then I will stop using them, however the oddity is that the current Outlook.com Mail does sync with WLM2012 now, so if they re changing the rest to become the same as Outlook.com mail, they should also Sync, unless they are messing with that as well.
I will stop using then and move to another email service who still retains the correct integration with WLM2012.
There is no other service that offers this three-pronged (mail/contacts/calendar) integration with Windows Live Mail, which was built specifically to synchronize (then) Hotmail (now) Microsoft Email accounts. The best you could hope for is mail synchronization alone via IMAP, which you can also implement in Windows Live Mail.
I am not bothered whether the Contacts/Calendar Sync or not as I currently don't use them. My contacts are PC based not web based.
Other Services such as Gmail and Yahoo still appear to retain their mail Sync including any folders created on or off line for those accounts, and work just fine with WLM2012
Stability Issues with the Windows Live Mail 2012 Update – KB3093594
We have received reports that the Windows Live Mail update- KB KB3093594, is causing stability issues for many of our customers running Windows Live Mail 2012.
Thank you for reporting this issue.
We have identified the root cause and are currently working on a fix that addresses the issue for impacted users on applicable platforms.
Please visit Update for Windows Live Essentials Mail 2012 or this thread for the latest updates.
***Update Dec 20^th^
Sorry for the delay in posting this update.
On Dec 17^th^we rereleased the Windows Live Mail update KB3093594. For users who had previously installed this update and were experiencing a crash when launching the Windows Live Mail app, please download and re-install KB3093594 and this issue should be resolved.
https://support.microsoft.com/kb/3093594
Some users have independently reported a separate issue with sync of mail with attachments that we continue to investigate.
Update 1 February 2016
(posted as Issues 3 under Known issues ... for KB3093594 rev. 6.0)
Some customers have reported other issues with the release on December 17, 2015. This update is no longer being offered while Microsoft investigates these issues further. Server interactions will remain supported during this investigation.
NB: links to http://www.microsoft.com/en-us/download/details.aspx?id=49486 will not work 
Windows for home | Other | Email and communications
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Anonymous
2016-01-07T19:27:46+00:00 -
Anonymous
2016-01-08T12:13:41+00:00 Windows 10 Users
There is no other service that offers this three-pronged (mail/contacts/calendar) integration with Windows Live Mail, which was built specifically to synchronize (then) Hotmail (now) Microsoft Email accounts. The best you could hope for is mail synchronization alone via IMAP, which you can also implement in Windows Live Mail.
Workaround it now seems possible thanks to; ¡Firedog and an outside source Jonathan Kay.com & next post.
Having studied this; when the changes take place; you will no longer be able to synchronize the account's mail folders using DeltaSync as seen via the account properties, server tab, see below;
New IMAP server settings as below;
Setting up a new IMAP account see ¡Firedog’s article Windows Live Mail and Outlook Mail
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Anonymous
2016-01-08T14:51:27+00:00 Workaround it now seems possible ...
With respect, Michael, that only works around one third of the problem - synchronizing mail folders. That's why I wrote the wiki article seven months ago explaining "how to work around part of the problem by using IMAP instead." Update KB3093594 is supposed to enable synchronization of mail, calendar and contacts using EAS, but it's so far unreliable. This thread originally dealt with the problems faced by Windows 10 users who installed the patch even though it was apparently not designed for W10 (Stability Issues is a euphemism for the program crashesthat Jonathan Kay writes about).
Incidentally, the server path shown in the HTTP account properties dialogue doesn't change with the update. It's only ever been there for information, and you can change it to whatever you like without it having any effect on sending and receiving. This account works flawlessly:
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Anonymous
2016-01-08T20:43:39+00:00 OT question from the Peanut Gallery @Noel: If a WLMail (v16.4.3528.0331) user is accessing an Outlook.com/Hotmail/MSN.com/Live.com account via POP3, doesn't care about synchronizing Calendar & Contacts, and does NOT sign-in to a Microsoft account/Live ID [1] when opening WLMail, is there any point to installing KB3093594?
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[1] <rant> Signing-in to a Microsoft account/Live ID and secure MS sites "recognizing" being signed-in has been pretty much a hit-or-miss proposition since early Dec-15 IMHO. For weeks I haven't been able to access, e.g., https://www.microsoft.com/security/portal/definitions/whatsnew.aspx ("Something went wrong and we can't sign you in right now...") but I could always access Outlook.com. Since yesterday, I could access the former but not the latter - so I don't know if my Outlook.com account's been converted to Outlook Mail (Preview) even though
KB3093592[typo] KB3093594 was offered as an Optional update starting today. </rant> -
Anonymous
2016-01-08T23:24:18+00:00 ... is there any point to installing KB3093594?
Not that I can see.
https://www.microsoft.com/security/portal/definitions/whatsnew.aspx
No problem for me. The same sort of thing happens regularly, though, and I can always (AFAIR) get there in the end by using IE InPrivate mode.
KB3093592 was offered as an Optional update starting today.
?