I "upgraded" WIN to 10 two days ago (forced by MS when I did not cancel automatic updates soon enough.  That in itself was Totally offensive and caused me a lot of extra work over the weekend).  The "upgrade" was more or less successful and the two accounts on my Windows Live Mail seemed to be working OK.

Until today, when, on closing, I got a message that Windows was reclaiming unused disc space.  It used to do that on Win 7 - probably 100s of times over the last 5 or 6 years, never with any problems.

HOWEVER, today, when I next opened Mail, it was totally empty.   Years and years of history just gone and most folders stated to be empty.   Yes it re-downloaded about 1000 incoming emails from one account which luckily kept them on server, but the secondary (but still highly important) account does not hold messages on the server and is still empty.  Likewise all the drafts, deleted, sent items, etc., are gone on both accounts and a few storage folders at the bottom of the list are also empty.  Fortunately I still have a calender and an address book.

Not good.  Obviously a major problem with Windows Live Mail on Windows 10.  Maybe I'd better change to Thunderbird (which was not affected).

To add insult to injury, Win 10 set me up for a windows newsgroup folder and filled it with a couple of hundred useless and totally unwanted news feeds.  Getting rid of that was not difficult.

What I need to know now, though, is how to salvage the Mail folders from the backup I took before "upgrading".   I'm sure they are hidden away in some folder and it should only be a matter of digging them out and connecting them up.   I did try reading the Mail help files but they do not specify the location.  And I also tried importing into the damaged mail program but it just informed me there were no files.  Did not even seem to be any in the recycle bin.

I wasted more than an hour talking to the Indian lady at Microsoft "Support" but she had no idea and kept ramming down my throat that it was a server problem and could not possibly be related to Win 10.   Not so, I'm afraid.  There seems to be a very serious problem between MSMail and Win 10 on my PC.

Here's hoping someone can help me find where to look for those backed up mail files.   Thanks in anticipation.